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 $202.36   11.102%   $224.826   $224.83   $224.85   $224.80  
  Purchase #2 $52.39   9.476%   $57.3545   $57.35   $57.35   $57.40  
  Purchase #3 $30.37   5.389%   $32.0066   $32.01   $32.00   $32.00  
  Purchase #4 $161.50   12.372%   $181.4808   $181.48   $181.50   $181.50  
  Purchase #5 $216.44   13.622%   $245.9235   $245.92   $245.90   $245.90  
  Purchase #6 $42.69   4.410%   $44.5726   $44.57   $44.55   $44.60  
  Purchase #7 $46.53   8.156%   $50.325   $50.33   $50.35   $50.30  
  7 purchase totals = $752.28       $836.4890   $836.49   $836.50   $836.50