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 $213.33   11.707%   $238.3045   $238.30   $238.30   $238.30  
  Purchase #2 $234.69   6.202%   $249.2455   $249.25   $249.25   $249.20  
  Purchase #3 $20.81   8.409%   $22.5599   $22.56   $22.55   $22.60  
  Purchase #4 $199.26   13.454%   $226.0684   $226.07   $226.05   $226.10  
  Purchase #5 $65.74   3.758%   $68.2105   $68.21   $68.20   $68.20  
  Purchase #6 $126.90   13.394%   $143.897   $143.90   $143.90   $143.90  
  Purchase #7 $133.97   9.281%   $146.4038   $146.40   $146.40   $146.40  
  7 purchase totals = $994.70       $1,094.6896   $1,094.69   $1,094.65   $1,094.70