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 $247.65   8.859%   $269.5893   $269.59   $269.60   $269.60  
  Purchase #2 $94.92   4.725%   $99.405   $99.41   $99.40   $99.40  
  Purchase #3 $160.88   10.558%   $177.8657   $177.87   $177.85   $177.90  
  Purchase #4 $28.93   11.864%   $32.3623   $32.36   $32.35   $32.40  
  Purchase #5 $87.99   9.382%   $96.2452   $96.25   $96.25   $96.20  
  Purchase #6 $43.90   6.524%   $46.764   $46.76   $46.75   $46.80  
  Purchase #7 $195.69   4.712%   $204.9109   $204.91   $204.90   $204.90  
  7 purchase totals = $859.96       $927.1424   $927.15   $927.10   $927.20