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 $232.36   3.711%   $240.9829   $240.98   $241.00   $241.00  
  Purchase #2 $234.25   11.243%   $260.5867   $260.59   $260.60   $260.60  
  Purchase #3 $241.96   7.405%   $259.8771   $259.88   $259.90   $259.90  
  Purchase #4 $207.98   9.804%   $228.3704   $228.37   $228.35   $228.40  
  Purchase #5 $84.54   3.799%   $87.7517   $87.75   $87.75   $87.80  
  Purchase #6 $201.82   11.640%   $225.3118   $225.31   $225.30   $225.30  
  Purchase #7 $181.87   10.524%   $201.01   $201.01   $201.00   $201.00  
  7 purchase totals = $1,384.78       $1,503.8906   $1,503.89   $1,503.90   $1,504.00