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 $73.71   5.322%   $77.6328   $77.63   $77.65   $77.60  
  Purchase #2 $71.71   5.142%   $75.3973   $75.40   $75.40   $75.40  
  Purchase #3 $25.49   4.818%   $26.7181   $26.72   $26.70   $26.70  
  Purchase #4 $186.39   7.484%   $200.3394   $200.34   $200.35   $200.30  
  Purchase #5 $61.47   7.376%   $66.004   $66.00   $66.00   $66.00  
  Purchase #6 $81.39   3.812%   $84.4926   $84.49   $84.50   $84.50  
  Purchase #7 $239.62   9.498%   $262.3791   $262.38   $262.40   $262.40  
  7 purchase totals = $739.78       $792.9633   $792.96   $793.00   $792.90