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 $41.29   11.415%   $46.0033   $46.00   $46.00   $46.00  
  Purchase #2 $120.50   4.520%   $125.9466   $125.95   $125.95   $125.90  
  Purchase #3 $116.66   9.114%   $127.2924   $127.29   $127.30   $127.30  
  Purchase #4 $228.86   6.169%   $242.9784   $242.98   $243.00   $243.00  
  Purchase #5 $131.72   4.686%   $137.8924   $137.89   $137.90   $137.90  
  Purchase #6 $67.62   4.798%   $70.8644   $70.86   $70.85   $70.90  
  Purchase #7 $244.94   6.442%   $260.719   $260.72   $260.70   $260.70  
  7 purchase totals = $951.59       $1,011.6965   $1,011.69   $1,011.70   $1,011.70