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 $58.54   8.106%   $63.2853   $63.29   $63.30   $63.30  
  Purchase #2 $133.83   3.226%   $138.1474   $138.15   $138.15   $138.10  
  Purchase #3 $140.70   13.728%   $160.0153   $160.02   $160.00   $160.00  
  Purchase #4 $60.54   11.166%   $67.2999   $67.30   $67.30   $67.30  
  Purchase #5 $238.64   6.153%   $253.3235   $253.32   $253.30   $253.30  
  Purchase #6 $114.62   5.132%   $120.5023   $120.50   $120.50   $120.50  
  Purchase #7 $136.90   10.675%   $151.5141   $151.51   $151.50   $151.50  
  7 purchase totals = $883.77       $954.0878   $954.09   $954.05   $954.00