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   8.134%   $101.4405   $101.44   $101.45   $101.40  
  Purchase #2 $72.89   7.122%   $78.0812   $78.08   $78.10   $78.10  
  Purchase #3 $34.70   4.748%   $36.3476   $36.35   $36.35   $36.30  
  Purchase #4 $82.98   3.374%   $85.7797   $85.78   $85.80   $85.80  
  Purchase #5 $239.71   12.475%   $269.6138   $269.61   $269.60   $269.60  
  Purchase #6 $220.86   8.655%   $239.9754   $239.98   $240.00   $240.00  
  Purchase #7 $154.89   12.679%   $174.5285   $174.53   $174.55   $174.50  
  7 purchase totals = $899.84       $985.7667   $985.77   $985.85   $985.70