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 $129.83   12.842%   $146.5028   $146.50   $146.50   $146.50  
  Purchase #2 $194.88   4.603%   $203.8503   $203.85   $203.85   $203.90  
  Purchase #3 $93.43   3.424%   $96.629   $96.63   $96.65   $96.60  
  Purchase #4 $60.99   9.252%   $66.6328   $66.63   $66.65   $66.60  
  Purchase #5 $41.50   9.857%   $45.5907   $45.59   $45.60   $45.60  
  Purchase #6 $118.64   3.791%   $123.1376   $123.14   $123.15   $123.10  
  Purchase #7 $141.53   13.765%   $161.0116   $161.01   $161.00   $161.00  
  7 purchase totals = $780.80       $843.3548   $843.35   $843.40   $843.30