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 $217.32   13.304%   $246.2323   $246.23   $246.25   $246.20  
  Purchase #2 $195.50   13.320%   $221.5406   $221.54   $221.55   $221.50  
  Purchase #3 $60.32   3.384%   $62.3612   $62.36   $62.35   $62.40  
  Purchase #4 $242.82   9.476%   $265.8296   $265.83   $265.85   $265.80  
  Purchase #5 $10.43   4.389%   $10.8878   $10.89   $10.90   $10.90  
  Purchase #6 $5.93   12.280%   $6.6582   $6.66   $6.65   $6.70  
  Purchase #7 $76.97   6.337%   $81.8476   $81.85   $81.85   $81.80  
  7 purchase totals = $809.29       $895.3573   $895.36   $895.40   $895.30