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 $185.38   8.402%   $200.9556   $200.96   $200.95   $201.00  
  Purchase #2 $228.81   6.658%   $244.0442   $244.04   $244.05   $244.00  
  Purchase #3 $188.92   8.760%   $205.4694   $205.47   $205.45   $205.50  
  Purchase #4 $167.67   6.309%   $178.2483   $178.25   $178.25   $178.20  
  Purchase #5 $40.54   5.239%   $42.6639   $42.66   $42.65   $42.70  
  Purchase #6 $7.55   11.731%   $8.4357   $8.44   $8.45   $8.40  
  Purchase #7 $169.80   12.446%   $190.9333   $190.93   $190.95   $190.90  
  7 purchase totals = $988.67       $1,070.7504   $1,070.75   $1,070.75   $1,070.70