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 $76.25   9.115%   $83.2002   $83.20   $83.20   $83.20  
  Purchase #2 $223.77   8.558%   $242.9202   $242.92   $242.90   $242.90  
  Purchase #3 $45.49   3.326%   $47.003   $47.00   $47.00   $47.00  
  Purchase #4 $37.40   10.299%   $41.2518   $41.25   $41.25   $41.30  
  Purchase #5 $37.46   13.742%   $42.6078   $42.61   $42.60   $42.60  
  Purchase #6 $163.75   10.374%   $180.7374   $180.74   $180.75   $180.70  
  Purchase #7 $87.83   7.746%   $94.6333   $94.63   $94.65   $94.60  
  7 purchase totals = $671.95       $732.3537   $732.35   $732.35   $732.30