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 $154.75   7.759%   $166.7571   $166.76   $166.75   $166.80  
  Purchase #2 $231.65   13.296%   $262.4502   $262.45   $262.45   $262.50  
  Purchase #3 $221.62   11.416%   $246.9201   $246.92   $246.90   $246.90  
  Purchase #4 $208.98   4.289%   $217.9432   $217.94   $217.95   $217.90  
  Purchase #5 $48.78   12.130%   $54.697   $54.70   $54.70   $54.70  
  Purchase #6 $124.51   7.457%   $133.7947   $133.79   $133.80   $133.80  
  Purchase #7 $64.31   13.694%   $73.1166   $73.12   $73.10   $73.10  
  7 purchase totals = $1,054.60       $1,155.6789   $1,155.68   $1,155.65   $1,155.70