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 $114.95   7.674%   $123.7713   $123.77   $123.75   $123.80  
  Purchase #2 $218.91   9.436%   $239.5663   $239.57   $239.55   $239.60  
  Purchase #3 $147.41   9.279%   $161.0882   $161.09   $161.10   $161.10  
  Purchase #4 $60.59   7.827%   $65.3324   $65.33   $65.35   $65.30  
  Purchase #5 $66.78   12.410%   $75.0674   $75.07   $75.05   $75.10  
  Purchase #6 $96.48   6.657%   $102.9027   $102.90   $102.90   $102.90  
  Purchase #7 $209.69   8.509%   $227.5325   $227.53   $227.55   $227.50  
  7 purchase totals = $914.81       $995.2608   $995.26   $995.25   $995.30