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 $68.84   12.591%   $77.5076   $77.51   $77.50   $77.50  
  Purchase #2 $209.25   13.398%   $237.2853   $237.29   $237.30   $237.30  
  Purchase #3 $127.42   9.616%   $139.6727   $139.67   $139.65   $139.70  
  Purchase #4 $219.32   6.776%   $234.1811   $234.18   $234.20   $234.20  
  Purchase #5 $22.41   12.226%   $25.1498   $25.15   $25.15   $25.10  
  Purchase #6 $204.26   12.755%   $230.3134   $230.31   $230.30   $230.30  
  Purchase #7 $11.96   8.126%   $12.9319   $12.93   $12.95   $12.90  
  7 purchase totals = $863.46       $957.0418   $957.04   $957.05   $957.00