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 $246.62   6.768%   $263.3112   $263.31   $263.30   $263.30  
  Purchase #2 $18.72   3.320%   $19.3415   $19.34   $19.35   $19.30  
  Purchase #3 $192.43   8.205%   $208.2189   $208.22   $208.20   $208.20  
  Purchase #4 $92.94   5.432%   $97.9885   $97.99   $98.00   $98.00  
  Purchase #5 $169.32   3.299%   $174.9059   $174.91   $174.90   $174.90  
  Purchase #6 $97.97   3.732%   $101.6262   $101.63   $101.65   $101.60  
  Purchase #7 $62.81   13.841%   $71.5035   $71.50   $71.50   $71.50  
  7 purchase totals = $880.81       $936.8957   $936.90   $936.90   $936.80