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 $232.99   10.563%   $257.6007   $257.60   $257.60   $257.60  
  Purchase #2 $109.69   13.681%   $124.6967   $124.70   $124.70   $124.70  
  Purchase #3 $140.82   7.229%   $150.9999   $151.00   $151.00   $151.00  
  Purchase #4 $97.36   3.453%   $100.7218   $100.72   $100.70   $100.70  
  Purchase #5 $127.97   4.240%   $133.3959   $133.40   $133.40   $133.40  
  Purchase #6 $51.52   9.307%   $56.315   $56.32   $56.30   $56.30  
  Purchase #7 $120.63   3.678%   $125.0668   $125.07   $125.05   $125.10  
  7 purchase totals = $880.98       $948.7968   $948.81   $948.75   $948.80