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 $167.80   12.616%   $188.9696   $188.97   $188.95   $189.00  
  Purchase #2 $172.67   8.567%   $187.4626   $187.46   $187.45   $187.50  
  Purchase #3 $60.90   13.334%   $69.0204   $69.02   $69.00   $69.00  
  Purchase #4 $234.31   11.111%   $260.3442   $260.34   $260.35   $260.30  
  Purchase #5 $90.78   5.525%   $95.7956   $95.80   $95.80   $95.80  
  Purchase #6 $237.45   9.183%   $259.255   $259.26   $259.25   $259.30  
  Purchase #7 $239.88   13.494%   $272.2494   $272.25   $272.25   $272.20  
  7 purchase totals = $1,203.79       $1,333.0968   $1,333.10   $1,333.05   $1,333.10