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 $76.60   11.308%   $85.2619   $85.26   $85.25   $85.30  
  Purchase #2 $48.43   13.294%   $54.8683   $54.87   $54.85   $54.90  
  Purchase #3 $36.70   7.408%   $39.4187   $39.42   $39.40   $39.40  
  Purchase #4 $93.49   5.487%   $98.6198   $98.62   $98.60   $98.60  
  Purchase #5 $48.66   7.381%   $52.2516   $52.25   $52.25   $52.30  
  Purchase #6 $49.76   5.761%   $52.6267   $52.63   $52.65   $52.60  
  Purchase #7 $13.34   9.206%   $14.5681   $14.57   $14.55   $14.60  
  7 purchase totals = $366.98       $397.6151   $397.62   $397.55   $397.70