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 $244.97   6.773%   $261.5618   $261.56   $261.55   $261.60  
  Purchase #2 $148.26   6.615%   $158.0674   $158.07   $158.05   $158.10  
  Purchase #3 $96.27   11.120%   $106.9752   $106.98   $107.00   $107.00  
  Purchase #4 $53.63   10.165%   $59.0815   $59.08   $59.10   $59.10  
  Purchase #5 $94.42   12.457%   $106.1819   $106.18   $106.20   $106.20  
  Purchase #6 $107.74   9.145%   $117.5928   $117.59   $117.60   $117.60  
  Purchase #7 $14.96   13.352%   $16.9575   $16.96   $16.95   $17.00  
  7 purchase totals = $760.25       $826.4181   $826.42   $826.45   $826.60