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 $86.66   9.258%   $94.683   $94.68   $94.70   $94.70  
  Purchase #2 $14.69   13.805%   $16.718   $16.72   $16.70   $16.70  
  Purchase #3 $118.30   4.738%   $123.9051   $123.91   $123.90   $123.90  
  Purchase #4 $174.63   5.865%   $184.872   $184.87   $184.85   $184.90  
  Purchase #5 $222.73   13.637%   $253.1037   $253.10   $253.10   $253.10  
  Purchase #6 $9.47   10.453%   $10.4599   $10.46   $10.45   $10.50  
  Purchase #7 $112.53   10.836%   $124.7238   $124.72   $124.70   $124.70  
  7 purchase totals = $739.01       $808.4655   $808.46   $808.40   $808.50