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 $58.82   3.676%   $60.9822   $60.98   $61.00   $61.00  
  Purchase #2 $167.34   12.789%   $188.7411   $188.74   $188.75   $188.70  
  Purchase #3 $155.48   5.423%   $163.9117   $163.91   $163.90   $163.90  
  Purchase #4 $125.67   8.837%   $136.7755   $136.78   $136.80   $136.80  
  Purchase #5 $114.62   6.424%   $121.9832   $121.98   $122.00   $122.00  
  Purchase #6 $153.54   4.500%   $160.4493   $160.45   $160.45   $160.40  
  Purchase #7 $33.79   11.209%   $37.5775   $37.58   $37.60   $37.60  
  7 purchase totals = $809.26       $870.4205   $870.42   $870.50   $870.40