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 $33.42   6.704%   $35.6605   $35.66   $35.65   $35.70  
  Purchase #2 $147.97   9.156%   $161.5181   $161.52   $161.50   $161.50  
  Purchase #3 $138.63   5.841%   $146.7274   $146.73   $146.75   $146.70  
  Purchase #4 $147.71   8.646%   $160.481   $160.48   $160.50   $160.50  
  Purchase #5 $81.88   11.423%   $91.2332   $91.23   $91.25   $91.20  
  Purchase #6 $205.53   4.281%   $214.3287   $214.33   $214.35   $214.30  
  Purchase #7 $227.49   9.581%   $249.2858   $249.29   $249.30   $249.30  
  7 purchase totals = $982.63       $1,059.2347   $1,059.24   $1,059.30   $1,059.20