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 $58.66   8.310%   $63.5346   $63.53   $63.55   $63.50  
  Purchase #2 $7.39   3.358%   $7.6382   $7.64   $7.65   $7.60  
  Purchase #3 $55.83   6.118%   $59.2457   $59.25   $59.25   $59.20  
  Purchase #4 $57.91   12.130%   $64.9345   $64.93   $64.95   $64.90  
  Purchase #5 $240.98   4.710%   $252.3302   $252.33   $252.35   $252.30  
  Purchase #6 $183.93   8.250%   $199.1042   $199.10   $199.10   $199.10  
  Purchase #7 $119.26   4.758%   $124.9344   $124.93   $124.95   $124.90  
  7 purchase totals = $723.96       $771.7218   $771.71   $771.80   $771.50