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 $86.48   5.412%   $91.1603   $91.16   $91.15   $91.20  
  Purchase #2 $57.89   13.349%   $65.6177   $65.62   $65.60   $65.60  
  Purchase #3 $46.70   6.164%   $49.5786   $49.58   $49.60   $49.60  
  Purchase #4 $123.68   8.510%   $134.2052   $134.21   $134.20   $134.20  
  Purchase #5 $137.29   7.465%   $147.5387   $147.54   $147.55   $147.50  
  Purchase #6 $141.59   13.582%   $160.8208   $160.82   $160.80   $160.80  
  Purchase #7 $210.38   8.184%   $227.5975   $227.60   $227.60   $227.60  
  7 purchase totals = $804.01       $876.5188   $876.53   $876.50   $876.50