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 $87.29   12.868%   $98.5225   $98.52   $98.50   $98.50  
  Purchase #2 $127.96   9.489%   $140.1021   $140.10   $140.10   $140.10  
  Purchase #3 $201.41   11.533%   $224.6386   $224.64   $224.65   $224.60  
  Purchase #4 $178.56   8.684%   $194.0662   $194.07   $194.05   $194.10  
  Purchase #5 $12.25   7.408%   $13.1575   $13.16   $13.15   $13.20  
  Purchase #6 $172.51   5.427%   $181.8721   $181.87   $181.85   $181.90  
  Purchase #7 $95.81   3.254%   $98.9277   $98.93   $98.95   $98.90  
  7 purchase totals = $875.79       $951.2867   $951.29   $951.25   $951.30