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 $54.57   12.796%   $61.5528   $61.55   $61.55   $61.60  
  Purchase #2 $247.44   7.207%   $265.273   $265.27   $265.25   $265.30  
  Purchase #3 $21.63   12.785%   $24.3954   $24.40   $24.40   $24.40  
  Purchase #4 $155.25   3.644%   $160.9073   $160.91   $160.90   $160.90  
  Purchase #5 $110.91   7.177%   $118.87   $118.87   $118.85   $118.90  
  Purchase #6 $115.38   12.364%   $129.6456   $129.65   $129.65   $129.60  
  Purchase #7 $148.29   6.331%   $157.6782   $157.68   $157.70   $157.70  
  7 purchase totals = $853.47       $918.3223   $918.33   $918.30   $918.40