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 $161.93   8.412%   $175.5516   $175.55   $175.55   $175.60  
  Purchase #2 $86.99   6.523%   $92.6644   $92.66   $92.65   $92.70  
  Purchase #3 $189.88   4.642%   $198.6942   $198.69   $198.70   $198.70  
  Purchase #4 $48.65   6.344%   $51.7364   $51.74   $51.75   $51.70  
  Purchase #5 $87.70   13.316%   $99.3781   $99.38   $99.40   $99.40  
  Purchase #6 $125.41   8.801%   $136.4473   $136.45   $136.45   $136.40  
  Purchase #7 $125.66   12.561%   $141.4442   $141.44   $141.45   $141.40  
  7 purchase totals = $826.22       $895.9162   $895.91   $895.95   $895.90