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 $82.91   11.550%   $92.4861   $92.49   $92.50   $92.50  
  Purchase #2 $146.65   9.844%   $161.0862   $161.09   $161.10   $161.10  
  Purchase #3 $240.49   3.871%   $249.7994   $249.80   $249.80   $249.80  
  Purchase #4 $88.64   5.498%   $93.5134   $93.51   $93.50   $93.50  
  Purchase #5 $131.99   4.657%   $138.1368   $138.14   $138.15   $138.10  
  Purchase #6 $235.76   10.564%   $260.6657   $260.67   $260.65   $260.70  
  Purchase #7 $241.81   12.638%   $272.3699   $272.37   $272.35   $272.40  
  7 purchase totals = $1,168.25       $1,268.0575   $1,268.07   $1,268.05   $1,268.10