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 $66.76   9.401%   $73.0361   $73.04   $73.05   $73.00  
  Purchase #2 $122.27   11.672%   $136.5414   $136.54   $136.55   $136.50  
  Purchase #3 $161.34   8.273%   $174.6877   $174.69   $174.70   $174.70  
  Purchase #4 $71.68   3.177%   $73.9573   $73.96   $73.95   $74.00  
  Purchase #5 $59.64   5.549%   $62.9494   $62.95   $62.95   $62.90  
  Purchase #6 $211.80   5.260%   $222.9407   $222.94   $222.95   $222.90  
  Purchase #7 $223.54   9.357%   $244.4566   $244.46   $244.45   $244.50  
  7 purchase totals = $917.03       $988.5692   $988.58   $988.60   $988.50