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 $118.95   7.257%   $127.5822   $127.58   $127.60   $127.60  
  Purchase #2 $85.74   9.204%   $93.6315   $93.63   $93.65   $93.60  
  Purchase #3 $32.35   12.185%   $36.2918   $36.29   $36.30   $36.30  
  Purchase #4 $244.25   6.534%   $260.2093   $260.21   $260.20   $260.20  
  Purchase #5 $54.35   5.556%   $57.3697   $57.37   $57.35   $57.40  
  Purchase #6 $150.58   8.639%   $163.5886   $163.59   $163.60   $163.60  
  Purchase #7 $149.94   6.438%   $159.5931   $159.59   $159.60   $159.60  
  7 purchase totals = $836.16       $898.2662   $898.26   $898.30   $898.30