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 $134.95   5.239%   $142.02   $142.02   $142.00   $142.00  
  Purchase #2 $203.44   5.698%   $215.032   $215.03   $215.05   $215.00  
  Purchase #3 $45.91   6.105%   $48.7128   $48.71   $48.70   $48.70  
  Purchase #4 $182.77   12.146%   $204.9692   $204.97   $204.95   $205.00  
  Purchase #5 $45.29   7.329%   $48.6093   $48.61   $48.60   $48.60  
  Purchase #6 $56.45   6.191%   $59.9448   $59.94   $59.95   $59.90  
  Purchase #7 $118.63   8.307%   $128.4846   $128.48   $128.50   $128.50  
  7 purchase totals = $787.44       $847.7727   $847.76   $847.75   $847.70