Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $163.93   12.721%   $184.7835   $184.78   $184.80   $184.80  
  Purchase #2 $133.48   10.846%   $147.9572   $147.96   $147.95   $148.00  
  Purchase #3 $182.89   12.219%   $205.2373   $205.24   $205.25   $205.20  
  Purchase #4 $208.73   8.172%   $225.7874   $225.79   $225.80   $225.80  
  Purchase #5 $247.90   4.685%   $259.5141   $259.51   $259.50   $259.50  
  Purchase #6 $186.88   3.434%   $193.2975   $193.30   $193.30   $193.30  
  Purchase #7 $215.39   6.589%   $229.582   $229.58   $229.60   $229.60  
  7 purchase totals = $1,339.20       $1,446.1590   $1,446.16   $1,446.20   $1,446.20