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 $61.85   8.758%   $67.2668   $67.27   $67.25   $67.30  
  Purchase #2 $81.43   12.289%   $91.4369   $91.44   $91.45   $91.40  
  Purchase #3 $41.57   12.830%   $46.9034   $46.90   $46.90   $46.90  
  Purchase #4 $204.35   10.383%   $225.5677   $225.57   $225.55   $225.60  
  Purchase #5 $217.87   12.551%   $245.2149   $245.21   $245.20   $245.20  
  Purchase #6 $142.54   4.309%   $148.682   $148.68   $148.70   $148.70  
  Purchase #7 $223.98   12.422%   $251.8028   $251.80   $251.80   $251.80  
  7 purchase totals = $973.59       $1,076.8745   $1,076.87   $1,076.85   $1,076.90