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 $86.65   12.386%   $97.3825   $97.38   $97.40   $97.40  
  Purchase #2 $14.28   13.154%   $16.1584   $16.16   $16.15   $16.20  
  Purchase #3 $52.81   4.214%   $55.0354   $55.04   $55.05   $55.00  
  Purchase #4 $63.69   5.103%   $66.9401   $66.94   $66.95   $66.90  
  Purchase #5 $88.90   12.667%   $100.161   $100.16   $100.15   $100.20  
  Purchase #6 $64.31   8.818%   $69.9809   $69.98   $70.00   $70.00  
  Purchase #7 $11.28   4.656%   $11.8052   $11.81   $11.80   $11.80  
  7 purchase totals = $381.92       $417.4635   $417.47   $417.50   $417.50