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 $154.58   5.442%   $162.9922   $162.99   $163.00   $163.00  
  Purchase #2 $118.64   4.481%   $123.9563   $123.96   $123.95   $124.00  
  Purchase #3 $205.64   5.851%   $217.672   $217.67   $217.65   $217.70  
  Purchase #4 $244.62   13.125%   $276.7264   $276.73   $276.75   $276.70  
  Purchase #5 $237.62   11.564%   $265.0984   $265.10   $265.10   $265.10  
  Purchase #6 $225.99   7.612%   $243.1924   $243.19   $243.20   $243.20  
  Purchase #7 $211.31   3.455%   $218.6108   $218.61   $218.60   $218.60  
  7 purchase totals = $1,398.40       $1,508.2485   $1,508.25   $1,508.25   $1,508.30