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 $108.89   7.112%   $116.6343   $116.63   $116.65   $116.60  
  Purchase #2 $171.79   4.591%   $179.6769   $179.68   $179.70   $179.70  
  Purchase #3 $91.66   3.607%   $94.9662   $94.97   $94.95   $95.00  
  Purchase #4 $140.77   11.174%   $156.4996   $156.50   $156.50   $156.50  
  Purchase #5 $132.71   7.369%   $142.4894   $142.49   $142.50   $142.50  
  Purchase #6 $126.95   13.355%   $143.9042   $143.90   $143.90   $143.90  
  Purchase #7 $175.62   8.395%   $190.3633   $190.36   $190.35   $190.40  
  7 purchase totals = $948.39       $1,024.5339   $1,024.53   $1,024.55   $1,024.60