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 $62.64   12.430%   $70.4262   $70.43   $70.45   $70.40  
  Purchase #2 $97.54   9.131%   $106.4464   $106.45   $106.45   $106.40  
  Purchase #3 $119.63   13.592%   $135.8901   $135.89   $135.90   $135.90  
  Purchase #4 $178.40   7.389%   $191.582   $191.58   $191.60   $191.60  
  Purchase #5 $196.46   13.574%   $223.1275   $223.13   $223.15   $223.10  
  Purchase #6 $87.25   12.532%   $98.1842   $98.18   $98.20   $98.20  
  Purchase #7 $139.88   6.497%   $148.968   $148.97   $148.95   $149.00  
  7 purchase totals = $881.80       $974.6244   $974.63   $974.70   $974.60