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 $58.55   5.814%   $61.9541   $61.95   $61.95   $62.00  
  Purchase #2 $98.65   7.836%   $106.3802   $106.38   $106.40   $106.40  
  Purchase #3 $50.94   6.184%   $54.0901   $54.09   $54.10   $54.10  
  Purchase #4 $173.41   11.534%   $193.4111   $193.41   $193.40   $193.40  
  Purchase #5 $94.41   4.409%   $98.5725   $98.57   $98.55   $98.60  
  Purchase #6 $6.55   4.722%   $6.8593   $6.86   $6.85   $6.90  
  Purchase #7 $26.81   12.196%   $30.0797   $30.08   $30.10   $30.10  
  7 purchase totals = $509.32       $551.3470   $551.34   $551.35   $551.50