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 $70.54   4.811%   $73.9337   $73.93   $73.95   $73.90  
  Purchase #2 $168.83   3.528%   $174.7863   $174.79   $174.80   $174.80  
  Purchase #3 $93.88   6.569%   $100.047   $100.05   $100.05   $100.00  
  Purchase #4 $60.90   3.779%   $63.2014   $63.20   $63.20   $63.20  
  Purchase #5 $55.83   10.276%   $61.5671   $61.57   $61.55   $61.60  
  Purchase #6 $195.92   6.245%   $208.1552   $208.16   $208.15   $208.20  
  Purchase #7 $239.64   12.175%   $268.8162   $268.82   $268.80   $268.80  
  7 purchase totals = $885.54       $950.5069   $950.52   $950.50   $950.50