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 $247.69   5.649%   $261.682   $261.68   $261.70   $261.70  
  Purchase #2 $12.82   7.623%   $13.7973   $13.80   $13.80   $13.80  
  Purchase #3 $154.95   3.276%   $160.0262   $160.03   $160.05   $160.00  
  Purchase #4 $27.38   12.579%   $30.8241   $30.82   $30.80   $30.80  
  Purchase #5 $179.54   8.341%   $194.5154   $194.52   $194.50   $194.50  
  Purchase #6 $34.64   3.719%   $35.9283   $35.93   $35.95   $35.90  
  Purchase #7 $98.41   4.223%   $102.5659   $102.57   $102.55   $102.60  
  7 purchase totals = $755.43       $799.3392   $799.35   $799.35   $799.30