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 $171.29   13.819%   $194.9606   $194.96   $194.95   $195.00  
  Purchase #2 $193.73   3.424%   $200.3633   $200.36   $200.35   $200.40  
  Purchase #3 $41.71   9.868%   $45.8259   $45.83   $45.85   $45.80  
  Purchase #4 $236.94   10.249%   $261.224   $261.22   $261.20   $261.20  
  Purchase #5 $227.27   5.238%   $239.1744   $239.17   $239.15   $239.20  
  Purchase #6 $101.86   5.527%   $107.4898   $107.49   $107.50   $107.50  
  Purchase #7 $130.90   10.210%   $144.2649   $144.26   $144.25   $144.30  
  7 purchase totals = $1,103.70       $1,193.3029   $1,193.29   $1,193.25   $1,193.40