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 $45.43   13.536%   $51.5794   $51.58   $51.60   $51.60  
  Purchase #2 $91.25   4.454%   $95.3143   $95.31   $95.30   $95.30  
  Purchase #3 $238.29   10.154%   $262.486   $262.49   $262.50   $262.50  
  Purchase #4 $57.78   5.552%   $60.9879   $60.99   $61.00   $61.00  
  Purchase #5 $185.67   13.810%   $211.311   $211.31   $211.30   $211.30  
  Purchase #6 $38.43   3.466%   $39.762   $39.76   $39.75   $39.80  
  Purchase #7 $150.61   8.229%   $163.0037   $163.00   $163.00   $163.00  
  7 purchase totals = $807.46       $884.4443   $884.44   $884.45   $884.50