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 $229.39   8.228%   $248.2642   $248.26   $248.25   $248.30  
  Purchase #2 $122.33   7.531%   $131.5427   $131.54   $131.55   $131.50  
  Purchase #3 $244.71   3.135%   $252.3817   $252.38   $252.40   $252.40  
  Purchase #4 $87.29   5.373%   $91.9801   $91.98   $92.00   $92.00  
  Purchase #5 $34.56   13.805%   $39.331   $39.33   $39.35   $39.30  
  Purchase #6 $224.81   11.197%   $249.982   $249.98   $250.00   $250.00  
  Purchase #7 $46.45   12.385%   $52.2028   $52.20   $52.20   $52.20  
  7 purchase totals = $989.54       $1,065.6845   $1,065.67   $1,065.75   $1,065.70