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 $62.38   5.468%   $65.7909   $65.79   $65.80   $65.80  
  Purchase #2 $179.64   12.186%   $201.5309   $201.53   $201.55   $201.50  
  Purchase #3 $75.91   13.404%   $86.085   $86.09   $86.10   $86.10  
  Purchase #4 $125.70   10.284%   $138.627   $138.63   $138.65   $138.60  
  Purchase #5 $111.60   11.852%   $124.8268   $124.83   $124.85   $124.80  
  Purchase #6 $244.98   7.735%   $263.9292   $263.93   $263.95   $263.90  
  Purchase #7 $170.68   10.252%   $188.1781   $188.18   $188.20   $188.20  
  7 purchase totals = $970.89       $1,068.9679   $1,068.98   $1,069.10   $1,068.90