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 $234.84   5.168%   $246.9765   $246.98   $247.00   $247.00  
  Purchase #2 $140.64   12.791%   $158.6293   $158.63   $158.65   $158.60  
  Purchase #3 $84.47   13.626%   $95.9799   $95.98   $96.00   $96.00  
  Purchase #4 $155.62   6.450%   $165.6575   $165.66   $165.65   $165.70  
  Purchase #5 $40.64   12.292%   $45.6355   $45.64   $45.65   $45.60  
  Purchase #6 $43.94   9.239%   $47.9996   $48.00   $48.00   $48.00  
  Purchase #7 $146.51   13.301%   $165.9973   $166.00   $166.00   $166.00  
  7 purchase totals = $846.66       $926.8756   $926.89   $926.95   $926.90