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 $89.76   6.759%   $95.8269   $95.83   $95.85   $95.80  
  Purchase #2 $151.82   8.125%   $164.1554   $164.16   $164.15   $164.20  
  Purchase #3 $51.86   12.392%   $58.2865   $58.29   $58.30   $58.30  
  Purchase #4 $64.91   6.724%   $69.2745   $69.27   $69.25   $69.30  
  Purchase #5 $190.97   5.763%   $201.9756   $201.98   $202.00   $202.00  
  Purchase #6 $51.36   10.184%   $56.5905   $56.59   $56.60   $56.60  
  Purchase #7 $94.64   6.682%   $100.9638   $100.96   $100.95   $101.00  
  7 purchase totals = $695.32       $747.0732   $747.08   $747.10   $747.20