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 $221.41   11.752%   $247.4301   $247.43   $247.45   $247.40  
  Purchase #2 $56.36   3.828%   $58.5175   $58.52   $58.50   $58.50  
  Purchase #3 $200.48   12.663%   $225.8668   $225.87   $225.85   $225.90  
  Purchase #4 $208.73   13.400%   $236.6998   $236.70   $236.70   $236.70  
  Purchase #5 $79.52   11.548%   $88.703   $88.70   $88.70   $88.70  
  Purchase #6 $80.88   11.610%   $90.2702   $90.27   $90.25   $90.30  
  Purchase #7 $44.62   9.823%   $49.003   $49.00   $49.00   $49.00  
  7 purchase totals = $892.00       $996.4904   $996.49   $996.45   $996.50