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 $70.90   6.110%   $75.232   $75.23   $75.25   $75.20  
  Purchase #2 $35.46   6.597%   $37.7993   $37.80   $37.80   $37.80  
  Purchase #3 $236.97   11.352%   $263.8708   $263.87   $263.85   $263.90  
  Purchase #4 $97.91   8.813%   $106.5388   $106.54   $106.55   $106.50  
  Purchase #5 $207.70   6.845%   $221.9171   $221.92   $221.90   $221.90  
  Purchase #6 $75.78   8.494%   $82.2168   $82.22   $82.20   $82.20  
  Purchase #7 $29.41   5.255%   $30.9555   $30.96   $30.95   $31.00  
  7 purchase totals = $754.13       $818.5303   $818.54   $818.50   $818.50