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 $93.81   11.152%   $104.2717   $104.27   $104.25   $104.30  
  Purchase #2 $213.98   11.106%   $237.7446   $237.74   $237.75   $237.70  
  Purchase #3 $140.85   11.186%   $156.6055   $156.61   $156.60   $156.60  
  Purchase #4 $62.86   4.716%   $65.8245   $65.82   $65.80   $65.80  
  Purchase #5 $234.34   12.482%   $263.5903   $263.59   $263.60   $263.60  
  Purchase #6 $193.38   13.233%   $218.97   $218.97   $218.95   $219.00  
  Purchase #7 $150.52   8.273%   $162.9725   $162.97   $162.95   $163.00  
  7 purchase totals = $1,089.74       $1,209.9791   $1,209.97   $1,209.90   $1,210.00