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 $62.76   4.371%   $65.5032   $65.50   $65.50   $65.50  
  Purchase #2 $194.53   4.340%   $202.9726   $202.97   $202.95   $203.00  
  Purchase #3 $136.84   5.352%   $144.1637   $144.16   $144.15   $144.20  
  Purchase #4 $149.36   9.409%   $163.4133   $163.41   $163.40   $163.40  
  Purchase #5 $33.30   9.701%   $36.5304   $36.53   $36.55   $36.50  
  Purchase #6 $39.44   3.666%   $40.8859   $40.89   $40.90   $40.90  
  Purchase #7 $239.35   12.551%   $269.3908   $269.39   $269.40   $269.40  
  7 purchase totals = $855.58       $922.8599   $922.85   $922.85   $922.90