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 $81.83   13.166%   $92.6037   $92.60   $92.60   $92.60  
  Purchase #2 $243.60   9.177%   $265.9552   $265.96   $265.95   $266.00  
  Purchase #3 $115.41   5.370%   $121.6075   $121.61   $121.60   $121.60  
  Purchase #4 $154.28   7.791%   $166.3   $166.30   $166.30   $166.30  
  Purchase #5 $114.99   7.434%   $123.5384   $123.54   $123.55   $123.50  
  Purchase #6 $157.51   10.386%   $173.869   $173.87   $173.85   $173.90  
  Purchase #7 $25.66   8.558%   $27.856   $27.86   $27.85   $27.90  
  7 purchase totals = $893.28       $971.7298   $971.74   $971.70   $971.80