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 $59.78   8.269%   $64.7232   $64.72   $64.70   $64.70  
  Purchase #2 $227.83   4.308%   $237.6449   $237.64   $237.65   $237.60  
  Purchase #3 $30.55   11.798%   $34.1543   $34.15   $34.15   $34.20  
  Purchase #4 $227.90   3.283%   $235.382   $235.38   $235.40   $235.40  
  Purchase #5 $99.31   7.541%   $106.799   $106.80   $106.80   $106.80  
  Purchase #6 $237.57   10.786%   $263.1943   $263.19   $263.20   $263.20  
  Purchase #7 $20.54   13.575%   $23.3283   $23.33   $23.35   $23.30  
  7 purchase totals = $903.48       $965.2260   $965.21   $965.25   $965.20