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 $237.27   11.277%   $264.0269   $264.03   $264.05   $264.00  
  Purchase #2 $227.49   9.395%   $248.8627   $248.86   $248.85   $248.90  
  Purchase #3 $29.36   4.282%   $30.6172   $30.62   $30.60   $30.60  
  Purchase #4 $202.70   6.802%   $216.4877   $216.49   $216.50   $216.50  
  Purchase #5 $23.90   9.356%   $26.1361   $26.14   $26.15   $26.10  
  Purchase #6 $29.84   10.549%   $32.9878   $32.99   $33.00   $33.00  
  Purchase #7 $59.65   5.320%   $62.8234   $62.82   $62.80   $62.80  
  7 purchase totals = $810.21       $881.9418   $881.95   $881.95   $881.90