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 $88.85   7.506%   $95.5191   $95.52   $95.50   $95.50  
  Purchase #2 $158.51   8.277%   $171.6299   $171.63   $171.65   $171.60  
  Purchase #3 $241.87   4.827%   $253.5451   $253.55   $253.55   $253.50  
  Purchase #4 $38.79   10.469%   $42.8509   $42.85   $42.85   $42.90  
  Purchase #5 $152.29   6.448%   $162.1097   $162.11   $162.10   $162.10  
  Purchase #6 $166.28   6.717%   $177.449   $177.45   $177.45   $177.40  
  Purchase #7 $25.71   8.307%   $27.8457   $27.85   $27.85   $27.80  
  7 purchase totals = $872.30       $930.9494   $930.96   $930.95   $930.80