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 $14.63   12.624%   $16.4769   $16.48   $16.50   $16.50  
  Purchase #2 $68.96   5.425%   $72.7011   $72.70   $72.70   $72.70  
  Purchase #3 $158.61   6.706%   $169.2464   $169.25   $169.25   $169.20  
  Purchase #4 $68.82   6.618%   $73.3745   $73.37   $73.35   $73.40  
  Purchase #5 $5.42   10.337%   $5.9803   $5.98   $6.00   $6.00  
  Purchase #6 $163.54   10.116%   $180.0837   $180.08   $180.10   $180.10  
  Purchase #7 $237.48   6.867%   $253.7878   $253.79   $253.80   $253.80  
  7 purchase totals = $717.46       $771.6507   $771.65   $771.70   $771.70