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 $85.76   9.261%   $93.7022   $93.70   $93.70   $93.70  
  Purchase #2 $131.99   8.448%   $143.1405   $143.14   $143.15   $143.10  
  Purchase #3 $128.56   9.604%   $140.9069   $140.91   $140.90   $140.90  
  Purchase #4 $49.69   12.493%   $55.8978   $55.90   $55.90   $55.90  
  Purchase #5 $166.76   3.649%   $172.8451   $172.85   $172.85   $172.80  
  Purchase #6 $52.68   7.281%   $56.5156   $56.52   $56.50   $56.50  
  Purchase #7 $131.63   5.601%   $139.0026   $139.00   $139.00   $139.00  
  7 purchase totals = $747.07       $802.0107   $802.02   $802.00   $801.90