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 $169.88   13.143%   $192.2073   $192.21   $192.20   $192.20  
  Purchase #2 $226.35   9.632%   $248.152   $248.15   $248.15   $248.20  
  Purchase #3 $27.71   13.196%   $31.3666   $31.37   $31.35   $31.40  
  Purchase #4 $27.43   10.424%   $30.2893   $30.29   $30.30   $30.30  
  Purchase #5 $210.25   9.860%   $230.9807   $230.98   $231.00   $231.00  
  Purchase #6 $176.90   12.394%   $198.825   $198.83   $198.85   $198.80  
  Purchase #7 $74.81   12.786%   $84.3752   $84.38   $84.40   $84.40  
  7 purchase totals = $913.33       $1,016.1961   $1,016.21   $1,016.25   $1,016.30