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 $228.36   7.588%   $245.688   $245.69   $245.70   $245.70  
  Purchase #2 $104.64   13.647%   $118.9202   $118.92   $118.90   $118.90  
  Purchase #3 $36.65   10.847%   $40.6254   $40.63   $40.65   $40.60  
  Purchase #4 $120.69   13.160%   $136.5728   $136.57   $136.55   $136.60  
  Purchase #5 $212.43   4.218%   $221.3903   $221.39   $221.40   $221.40  
  Purchase #6 $222.67   11.201%   $247.6113   $247.61   $247.60   $247.60  
  Purchase #7 $245.48   4.731%   $257.0937   $257.09   $257.10   $257.10  
  7 purchase totals = $1,170.92       $1,267.9017   $1,267.90   $1,267.90   $1,267.90