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 $166.79   9.656%   $182.8952   $182.90   $182.90   $182.90  
  Purchase #2 $24.40   4.758%   $25.561   $25.56   $25.55   $25.60  
  Purchase #3 $144.35   6.411%   $153.6043   $153.60   $153.60   $153.60  
  Purchase #4 $59.88   11.439%   $66.7297   $66.73   $66.75   $66.70  
  Purchase #5 $198.95   4.217%   $207.3397   $207.34   $207.35   $207.30  
  Purchase #6 $163.84   6.145%   $173.908   $173.91   $173.90   $173.90  
  Purchase #7 $108.32   12.271%   $121.6119   $121.61   $121.60   $121.60  
  7 purchase totals = $866.53       $931.6498   $931.65   $931.65   $931.60