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 $241.74   13.222%   $273.7029   $273.70   $273.70   $273.70  
  Purchase #2 $92.25   5.530%   $97.3514   $97.35   $97.35   $97.40  
  Purchase #3 $20.80   9.626%   $22.8022   $22.80   $22.80   $22.80  
  Purchase #4 $222.38   5.201%   $233.946   $233.95   $233.95   $233.90  
  Purchase #5 $54.95   11.539%   $61.2907   $61.29   $61.30   $61.30  
  Purchase #6 $244.48   3.226%   $252.3669   $252.37   $252.35   $252.40  
  Purchase #7 $250.82   5.219%   $263.9103   $263.91   $263.90   $263.90  
  7 purchase totals = $1,127.42       $1,205.3704   $1,205.37   $1,205.35   $1,205.40