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 $81.91   13.846%   $93.2513   $93.25   $93.25   $93.30  
  Purchase #2 $230.26   7.427%   $247.3614   $247.36   $247.35   $247.40  
  Purchase #3 $31.54   9.530%   $34.5458   $34.55   $34.55   $34.50  
  Purchase #4 $10.58   8.620%   $11.492   $11.49   $11.50   $11.50  
  Purchase #5 $91.86   10.289%   $101.3115   $101.31   $101.30   $101.30  
  Purchase #6 $181.49   7.504%   $195.109   $195.11   $195.10   $195.10  
  Purchase #7 $192.85   10.560%   $213.215   $213.22   $213.20   $213.20  
  7 purchase totals = $820.49       $896.2860   $896.29   $896.25   $896.30