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 $206.73   13.248%   $234.1176   $234.12   $234.10   $234.10  
  Purchase #2 $51.74   4.667%   $54.1547   $54.15   $54.15   $54.20  
  Purchase #3 $45.28   5.802%   $47.9071   $47.91   $47.90   $47.90  
  Purchase #4 $29.81   13.755%   $33.9104   $33.91   $33.90   $33.90  
  Purchase #5 $221.44   5.805%   $234.2946   $234.29   $234.30   $234.30  
  Purchase #6 $240.71   9.618%   $263.8615   $263.86   $263.85   $263.90  
  Purchase #7 $26.87   7.855%   $28.9806   $28.98   $29.00   $29.00  
  7 purchase totals = $822.58       $897.2265   $897.22   $897.20   $897.30