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 $8.75   4.641%   $9.1561   $9.16   $9.15   $9.20  
  Purchase #2 $187.52   3.711%   $194.4789   $194.48   $194.50   $194.50  
  Purchase #3 $156.96   4.568%   $164.1299   $164.13   $164.15   $164.10  
  Purchase #4 $94.87   11.593%   $105.8683   $105.87   $105.85   $105.90  
  Purchase #5 $94.36   10.357%   $104.1329   $104.13   $104.15   $104.10  
  Purchase #6 $128.45   7.711%   $138.3548   $138.35   $138.35   $138.40  
  Purchase #7 $140.46   4.785%   $147.181   $147.18   $147.20   $147.20  
  7 purchase totals = $811.37       $863.3019   $863.30   $863.35   $863.40