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 $42.81   3.405%   $44.2677   $44.27   $44.25   $44.30  
  Purchase #2 $84.90   3.778%   $88.1075   $88.11   $88.10   $88.10  
  Purchase #3 $6.88   11.582%   $7.6768   $7.68   $7.70   $7.70  
  Purchase #4 $163.76   5.375%   $172.5621   $172.56   $172.55   $172.60  
  Purchase #5 $23.55   7.853%   $25.3994   $25.40   $25.40   $25.40  
  Purchase #6 $8.85   9.459%   $9.6871   $9.69   $9.70   $9.70  
  Purchase #7 $86.56   13.692%   $98.4118   $98.41   $98.40   $98.40  
  7 purchase totals = $417.31       $446.1124   $446.12   $446.10   $446.20