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 $60.70   3.785%   $62.9975   $63.00   $63.00   $63.00  
  Purchase #2 $9.81   8.125%   $10.6071   $10.61   $10.60   $10.60  
  Purchase #3 $119.36   7.273%   $128.0411   $128.04   $128.05   $128.00  
  Purchase #4 $42.47   4.236%   $44.269   $44.27   $44.25   $44.30  
  Purchase #5 $26.80   10.534%   $29.6231   $29.62   $29.60   $29.60  
  Purchase #6 $153.39   6.218%   $162.9278   $162.93   $162.95   $162.90  
  Purchase #7 $20.35   10.722%   $22.5319   $22.53   $22.55   $22.50  
  7 purchase totals = $432.88       $460.9975   $461.00   $461.00   $460.90