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 $81.62   5.347%   $85.9842   $85.98   $86.00   $86.00  
  Purchase #2 $37.54   8.149%   $40.5991   $40.60   $40.60   $40.60  
  Purchase #3 $96.93   7.789%   $104.4799   $104.48   $104.50   $104.50  
  Purchase #4 $176.78   4.282%   $184.3497   $184.35   $184.35   $184.30  
  Purchase #5 $179.95   4.674%   $188.3609   $188.36   $188.35   $188.40  
  Purchase #6 $74.84   3.849%   $77.7206   $77.72   $77.70   $77.70  
  Purchase #7 $69.29   7.799%   $74.6939   $74.69   $74.70   $74.70  
  7 purchase totals = $716.95       $756.1883   $756.18   $756.20   $756.20