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 $57.63   3.224%   $59.488   $59.49   $59.50   $59.50  
  Purchase #2 $250.78   11.127%   $278.6843   $278.68   $278.70   $278.70  
  Purchase #3 $57.33   6.790%   $61.2227   $61.22   $61.20   $61.20  
  Purchase #4 $44.75   7.324%   $48.0275   $48.03   $48.05   $48.00  
  Purchase #5 $210.92   4.524%   $220.462   $220.46   $220.45   $220.50  
  Purchase #6 $11.72   13.737%   $13.33   $13.33   $13.35   $13.30  
  Purchase #7 $74.25   13.852%   $84.5351   $84.54   $84.55   $84.50  
  7 purchase totals = $707.38       $765.7496   $765.75   $765.80   $765.70