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 $71.56   6.862%   $76.4704   $76.47   $76.45   $76.50  
  Purchase #2 $118.88   6.566%   $126.6857   $126.69   $126.70   $126.70  
  Purchase #3 $167.80   3.662%   $173.9448   $173.94   $173.95   $173.90  
  Purchase #4 $145.72   3.332%   $150.5754   $150.58   $150.60   $150.60  
  Purchase #5 $81.64   8.857%   $88.8709   $88.87   $88.85   $88.90  
  Purchase #6 $67.73   12.195%   $75.9897   $75.99   $76.00   $76.00  
  Purchase #7 $245.97   5.139%   $258.6104   $258.61   $258.60   $258.60  
  7 purchase totals = $899.30       $951.1473   $951.15   $951.15   $951.20