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 $33.79   3.533%   $34.9838   $34.98   $35.00   $35.00  
  Purchase #2 $177.32   7.862%   $191.2609   $191.26   $191.25   $191.30  
  Purchase #3 $232.37   9.254%   $253.8735   $253.87   $253.85   $253.90  
  Purchase #4 $72.93   7.581%   $78.4588   $78.46   $78.45   $78.50  
  Purchase #5 $24.77   4.486%   $25.8812   $25.88   $25.90   $25.90  
  Purchase #6 $149.45   5.276%   $157.335   $157.34   $157.35   $157.30  
  Purchase #7 $207.60   5.858%   $219.7612   $219.76   $219.75   $219.80  
  7 purchase totals = $898.23       $961.5544   $961.55   $961.55   $961.70