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 $84.82   12.579%   $95.4895   $95.49   $95.50   $95.50  
  Purchase #2 $97.27   8.347%   $105.3891   $105.39   $105.40   $105.40  
  Purchase #3 $5.91   4.712%   $6.1885   $6.19   $6.20   $6.20  
  Purchase #4 $192.94   3.237%   $199.1855   $199.19   $199.20   $199.20  
  Purchase #5 $221.42   12.210%   $248.4554   $248.46   $248.45   $248.50  
  Purchase #6 $87.63   3.408%   $90.6164   $90.62   $90.60   $90.60  
  Purchase #7 $61.80   11.409%   $68.8508   $68.85   $68.85   $68.90  
  7 purchase totals = $751.79       $814.1752   $814.19   $814.20   $814.30