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 $48.29   8.829%   $52.5535   $52.55   $52.55   $52.60  
  Purchase #2 $67.57   8.532%   $73.3351   $73.34   $73.35   $73.30  
  Purchase #3 $109.83   8.715%   $119.4017   $119.40   $119.40   $119.40  
  Purchase #4 $29.69   13.823%   $33.794   $33.79   $33.80   $33.80  
  Purchase #5 $158.54   10.753%   $175.5878   $175.59   $175.60   $175.60  
  Purchase #6 $145.47   10.845%   $161.2462   $161.25   $161.25   $161.20  
  Purchase #7 $216.33   8.752%   $235.2632   $235.26   $235.25   $235.30  
  7 purchase totals = $775.72       $851.1815   $851.18   $851.20   $851.20