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 $62.30   11.662%   $69.5654   $69.57   $69.55   $69.60  
  Purchase #2 $101.78   6.465%   $108.3601   $108.36   $108.35   $108.40  
  Purchase #3 $92.59   6.780%   $98.8676   $98.87   $98.85   $98.90  
  Purchase #4 $200.53   3.336%   $207.2197   $207.22   $207.20   $207.20  
  Purchase #5 $35.60   13.867%   $40.5367   $40.54   $40.55   $40.50  
  Purchase #6 $35.52   10.269%   $39.1675   $39.17   $39.15   $39.20  
  Purchase #7 $30.94   9.677%   $33.9341   $33.93   $33.95   $33.90  
  7 purchase totals = $559.26       $597.6511   $597.66   $597.60   $597.70