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 $115.67   3.433%   $119.641   $119.64   $119.65   $119.60  
  Purchase #2 $115.96   11.389%   $129.1667   $129.17   $129.15   $129.20  
  Purchase #3 $49.84   7.573%   $53.6144   $53.61   $53.60   $53.60  
  Purchase #4 $96.27   11.704%   $107.5374   $107.54   $107.55   $107.50  
  Purchase #5 $171.46   11.533%   $191.2345   $191.23   $191.25   $191.20  
  Purchase #6 $143.87   13.650%   $163.5083   $163.51   $163.50   $163.50  
  Purchase #7 $67.36   6.353%   $71.6394   $71.64   $71.65   $71.60  
  7 purchase totals = $760.43       $836.3417   $836.34   $836.35   $836.20