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 $109.90   8.291%   $119.0118   $119.01   $119.00   $119.00  
  Purchase #2 $79.72   9.475%   $87.2735   $87.27   $87.25   $87.30  
  Purchase #3 $211.54   6.214%   $224.6851   $224.69   $224.70   $224.70  
  Purchase #4 $180.46   3.592%   $186.9421   $186.94   $186.95   $186.90  
  Purchase #5 $24.30   9.230%   $26.5429   $26.54   $26.55   $26.50  
  Purchase #6 $80.57   7.563%   $86.6635   $86.66   $86.65   $86.70  
  Purchase #7 $195.98   12.408%   $220.2972   $220.30   $220.30   $220.30  
  7 purchase totals = $882.47       $951.4161   $951.41   $951.40   $951.40