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 $84.98   12.532%   $95.6297   $95.63   $95.65   $95.60  
  Purchase #2 $55.60   7.402%   $59.7155   $59.72   $59.70   $59.70  
  Purchase #3 $11.55   5.673%   $12.2052   $12.21   $12.20   $12.20  
  Purchase #4 $181.96   3.507%   $188.3413   $188.34   $188.35   $188.30  
  Purchase #5 $48.28   8.122%   $52.2013   $52.20   $52.20   $52.20  
  Purchase #6 $62.71   11.179%   $69.7204   $69.72   $69.70   $69.70  
  Purchase #7 $16.61   12.119%   $18.623   $18.62   $18.60   $18.60  
  7 purchase totals = $461.69       $496.4364   $496.44   $496.40   $496.30