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 $241.80   9.631%   $265.0878   $265.09   $265.10   $265.10  
  Purchase #2 $188.47   11.618%   $210.3664   $210.37   $210.35   $210.40  
  Purchase #3 $96.92   10.227%   $106.832   $106.83   $106.85   $106.80  
  Purchase #4 $133.27   5.116%   $140.0881   $140.09   $140.10   $140.10  
  Purchase #5 $86.29   6.455%   $91.86   $91.86   $91.85   $91.90  
  Purchase #6 $121.34   12.575%   $136.5985   $136.60   $136.60   $136.60  
  Purchase #7 $188.96   8.424%   $204.878   $204.88   $204.90   $204.90  
  7 purchase totals = $1,057.05       $1,155.7108   $1,155.72   $1,155.75   $1,155.80