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 $53.91   5.498%   $56.874   $56.87   $56.85   $56.90  
  Purchase #2 $59.38   7.306%   $63.7183   $63.72   $63.70   $63.70  
  Purchase #3 $125.81   5.641%   $132.9069   $132.91   $132.90   $132.90  
  Purchase #4 $194.93   12.809%   $219.8986   $219.90   $219.90   $219.90  
  Purchase #5 $219.25   9.513%   $240.1073   $240.11   $240.10   $240.10  
  Purchase #6 $61.79   10.695%   $68.3984   $68.40   $68.40   $68.40  
  Purchase #7 $101.65   3.777%   $105.4893   $105.49   $105.50   $105.50  
  7 purchase totals = $816.72       $887.3928   $887.40   $887.35   $887.40