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 $210.98   11.219%   $234.6498   $234.65   $234.65   $234.60  
  Purchase #2 $25.42   7.626%   $27.3585   $27.36   $27.35   $27.40  
  Purchase #3 $31.25   9.174%   $34.1169   $34.12   $34.10   $34.10  
  Purchase #4 $20.88   9.458%   $22.8548   $22.85   $22.85   $22.90  
  Purchase #5 $204.61   3.159%   $211.0736   $211.07   $211.05   $211.10  
  Purchase #6 $192.67   3.341%   $199.1071   $199.11   $199.10   $199.10  
  Purchase #7 $60.29   8.800%   $65.5955   $65.60   $65.60   $65.60  
  7 purchase totals = $746.10       $794.7562   $794.76   $794.70   $794.80