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 $76.75   11.161%   $85.3161   $85.32   $85.30   $85.30  
  Purchase #2 $92.37   3.587%   $95.6833   $95.68   $95.70   $95.70  
  Purchase #3 $168.67   8.119%   $182.3643   $182.36   $182.35   $182.40  
  Purchase #4 $88.80   12.505%   $99.9044   $99.90   $99.90   $99.90  
  Purchase #5 $160.81   7.660%   $173.128   $173.13   $173.15   $173.10  
  Purchase #6 $82.75   5.143%   $87.0058   $87.01   $87.00   $87.00  
  Purchase #7 $53.84   5.516%   $56.8098   $56.81   $56.80   $56.80  
  7 purchase totals = $723.99       $780.2117   $780.21   $780.20   $780.20