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 $208.85   11.466%   $232.7967   $232.80   $232.80   $232.80  
  Purchase #2 $153.35   9.753%   $168.3062   $168.31   $168.30   $168.30  
  Purchase #3 $65.74   5.563%   $69.3971   $69.40   $69.40   $69.40  
  Purchase #4 $236.96   3.624%   $245.5474   $245.55   $245.55   $245.50  
  Purchase #5 $110.57   8.496%   $119.964   $119.96   $119.95   $120.00  
  Purchase #6 $33.72   3.229%   $34.8088   $34.81   $34.80   $34.80  
  Purchase #7 $120.63   5.395%   $127.138   $127.14   $127.15   $127.10  
  7 purchase totals = $929.82       $997.9582   $997.97   $997.95   $997.90