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 $204.95   13.710%   $233.0486   $233.05   $233.05   $233.00  
  Purchase #2 $153.36   10.213%   $169.0227   $169.02   $169.00   $169.00  
  Purchase #3 $55.43   8.220%   $59.9863   $59.99   $60.00   $60.00  
  Purchase #4 $120.86   6.262%   $128.4283   $128.43   $128.45   $128.40  
  Purchase #5 $52.39   8.346%   $56.7625   $56.76   $56.75   $56.80  
  Purchase #6 $42.97   4.203%   $44.776   $44.78   $44.80   $44.80  
  Purchase #7 $133.45   3.320%   $137.8805   $137.88   $137.90   $137.90  
  7 purchase totals = $763.41       $829.9049   $829.91   $829.95   $829.90