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 $62.61   11.125%   $69.5754   $69.58   $69.60   $69.60  
  Purchase #2 $138.82   6.820%   $148.2875   $148.29   $148.30   $148.30  
  Purchase #3 $72.55   13.691%   $82.4828   $82.48   $82.50   $82.50  
  Purchase #4 $168.69   3.778%   $175.0631   $175.06   $175.05   $175.10  
  Purchase #5 $62.98   6.284%   $66.9377   $66.94   $66.95   $66.90  
  Purchase #6 $174.68   10.603%   $193.2013   $193.20   $193.20   $193.20  
  Purchase #7 $87.30   7.400%   $93.7602   $93.76   $93.75   $93.80  
  7 purchase totals = $767.63       $829.3080   $829.31   $829.35   $829.40