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 $235.48   8.270%   $254.9542   $254.95   $254.95   $255.00  
  Purchase #2 $18.47   11.709%   $20.6327   $20.63   $20.65   $20.60  
  Purchase #3 $9.37   12.770%   $10.5665   $10.57   $10.55   $10.60  
  Purchase #4 $204.34   7.409%   $219.4796   $219.48   $219.50   $219.50  
  Purchase #5 $29.86   4.233%   $31.124   $31.12   $31.10   $31.10  
  Purchase #6 $219.92   13.808%   $250.2866   $250.29   $250.30   $250.30  
  Purchase #7 $153.69   13.175%   $173.9387   $173.94   $173.95   $173.90  
  7 purchase totals = $871.13       $960.9823   $960.98   $961.00   $961.00