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 $56.67   13.199%   $64.1499   $64.15   $64.15   $64.10  
  Purchase #2 $175.91   8.199%   $190.3329   $190.33   $190.35   $190.30  
  Purchase #3 $93.48   11.170%   $103.9217   $103.92   $103.90   $103.90  
  Purchase #4 $67.25   9.358%   $73.5433   $73.54   $73.55   $73.50  
  Purchase #5 $180.55   8.414%   $195.7415   $195.74   $195.75   $195.70  
  Purchase #6 $165.40   13.262%   $187.3353   $187.34   $187.35   $187.30  
  Purchase #7 $247.78   12.116%   $277.801   $277.80   $277.80   $277.80  
  7 purchase totals = $987.04       $1,092.8256   $1,092.82   $1,092.85   $1,092.60