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 $196.93   8.228%   $213.1334   $213.13   $213.15   $213.10  
  Purchase #2 $51.65   5.253%   $54.3632   $54.36   $54.35   $54.40  
  Purchase #3 $80.93   5.506%   $85.386   $85.39   $85.40   $85.40  
  Purchase #4 $71.43   5.575%   $75.4122   $75.41   $75.40   $75.40  
  Purchase #5 $101.89   6.873%   $108.8929   $108.89   $108.90   $108.90  
  Purchase #6 $26.43   3.628%   $27.3889   $27.39   $27.40   $27.40  
  Purchase #7 $214.34   8.291%   $232.1109   $232.11   $232.10   $232.10  
  7 purchase totals = $743.60       $796.6875   $796.68   $796.70   $796.70