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 $60.94   4.165%   $63.4782   $63.48   $63.50   $63.50  
  Purchase #2 $165.32   6.191%   $175.555   $175.56   $175.55   $175.60  
  Purchase #3 $121.63   10.480%   $134.3768   $134.38   $134.40   $134.40  
  Purchase #4 $229.56   7.639%   $247.0961   $247.10   $247.10   $247.10  
  Purchase #5 $61.81   8.122%   $66.8302   $66.83   $66.85   $66.80  
  Purchase #6 $75.32   11.549%   $84.0187   $84.02   $84.00   $84.00  
  Purchase #7 $151.91   13.633%   $172.6199   $172.62   $172.60   $172.60  
  7 purchase totals = $866.49       $943.9749   $943.99   $944.00   $944.00