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 $234.40   8.653%   $254.6826   $254.68   $254.70   $254.70  
  Purchase #2 $85.94   12.752%   $96.8991   $96.90   $96.90   $96.90  
  Purchase #3 $119.46   11.473%   $133.1656   $133.17   $133.15   $133.20  
  Purchase #4 $57.38   9.120%   $62.6131   $62.61   $62.60   $62.60  
  Purchase #5 $175.69   9.203%   $191.8588   $191.86   $191.85   $191.90  
  Purchase #6 $175.51   6.216%   $186.4197   $186.42   $186.40   $186.40  
  Purchase #7 $167.73   7.619%   $180.5093   $180.51   $180.50   $180.50  
  7 purchase totals = $1,016.11       $1,106.1482   $1,106.15   $1,106.10   $1,106.20