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 $206.79   6.243%   $219.6999   $219.70   $219.70   $219.70  
  Purchase #2 $215.61   4.832%   $226.0283   $226.03   $226.05   $226.00  
  Purchase #3 $158.30   7.561%   $170.2691   $170.27   $170.25   $170.30  
  Purchase #4 $33.73   4.360%   $35.2006   $35.20   $35.20   $35.20  
  Purchase #5 $155.70   12.118%   $174.5677   $174.57   $174.55   $174.60  
  Purchase #6 $208.38   13.217%   $235.9216   $235.92   $235.90   $235.90  
  Purchase #7 $97.64   8.199%   $105.6455   $105.65   $105.65   $105.60  
  7 purchase totals = $1,076.15       $1,167.3327   $1,167.34   $1,167.30   $1,167.30