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 $200.43   12.760%   $226.0049   $226.00   $226.00   $226.00  
  Purchase #2 $43.84   6.340%   $46.6195   $46.62   $46.60   $46.60  
  Purchase #3 $52.83   5.255%   $55.6062   $55.61   $55.60   $55.60  
  Purchase #4 $175.37   3.756%   $181.9569   $181.96   $181.95   $182.00  
  Purchase #5 $73.67   3.612%   $76.331   $76.33   $76.35   $76.30  
  Purchase #6 $119.55   12.861%   $134.9253   $134.93   $134.95   $134.90  
  Purchase #7 $81.70   3.160%   $84.2817   $84.28   $84.30   $84.30  
  7 purchase totals = $747.39       $805.7255   $805.73   $805.75   $805.70