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 $83.82   13.753%   $95.3478   $95.35   $95.35   $95.30  
  Purchase #2 $93.96   6.475%   $100.0439   $100.04   $100.05   $100.00  
  Purchase #3 $13.54   11.168%   $15.0521   $15.05   $15.05   $15.10  
  Purchase #4 $53.76   7.294%   $57.6813   $57.68   $57.70   $57.70  
  Purchase #5 $9.84   9.108%   $10.7362   $10.74   $10.75   $10.70  
  Purchase #6 $245.35   6.320%   $260.8561   $260.86   $260.85   $260.90  
  Purchase #7 $60.69   9.156%   $66.2468   $66.25   $66.25   $66.20  
  7 purchase totals = $560.96       $605.9642   $605.97   $606.00   $605.90