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 $190.89   11.606%   $213.0447   $213.04   $213.05   $213.00  
  Purchase #2 $55.94   10.668%   $61.9077   $61.91   $61.90   $61.90  
  Purchase #3 $109.91   7.529%   $118.1851   $118.19   $118.20   $118.20  
  Purchase #4 $107.31   3.351%   $110.906   $110.91   $110.90   $110.90  
  Purchase #5 $164.79   6.689%   $175.8128   $175.81   $175.80   $175.80  
  Purchase #6 $95.72   3.116%   $98.7026   $98.70   $98.70   $98.70  
  Purchase #7 $182.82   8.120%   $197.665   $197.67   $197.65   $197.70  
  7 purchase totals = $907.38       $976.2239   $976.23   $976.20   $976.20