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 $64.32   10.134%   $70.8382   $70.84   $70.85   $70.80  
  Purchase #2 $158.89   7.206%   $170.3396   $170.34   $170.35   $170.30  
  Purchase #3 $157.55   10.664%   $174.3511   $174.35   $174.35   $174.40  
  Purchase #4 $227.71   3.290%   $235.2017   $235.20   $235.20   $235.20  
  Purchase #5 $247.86   3.560%   $256.6838   $256.68   $256.70   $256.70  
  Purchase #6 $113.47   9.271%   $123.9898   $123.99   $124.00   $124.00  
  Purchase #7 $165.39   3.450%   $171.096   $171.10   $171.10   $171.10  
  7 purchase totals = $1,135.19       $1,202.5002   $1,202.50   $1,202.55   $1,202.50