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 $183.65   11.647%   $205.0397   $205.04   $205.05   $205.00  
  Purchase #2 $117.69   6.658%   $125.5258   $125.53   $125.55   $125.50  
  Purchase #3 $184.60   5.723%   $195.1647   $195.16   $195.15   $195.20  
  Purchase #4 $46.52   7.302%   $49.9169   $49.92   $49.90   $49.90  
  Purchase #5 $144.53   4.661%   $151.2665   $151.27   $151.25   $151.30  
  Purchase #6 $200.96   9.866%   $220.7867   $220.79   $220.80   $220.80  
  Purchase #7 $226.33   6.520%   $241.0867   $241.09   $241.10   $241.10  
  7 purchase totals = $1,104.28       $1,188.7870   $1,188.80   $1,188.80   $1,188.80