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 $61.78   11.541%   $68.91   $68.91   $68.90   $68.90  
  Purchase #2 $202.34   7.169%   $216.8458   $216.85   $216.85   $216.80  
  Purchase #3 $241.91   3.678%   $250.8074   $250.81   $250.80   $250.80  
  Purchase #4 $132.25   6.809%   $141.2549   $141.25   $141.25   $141.30  
  Purchase #5 $240.39   6.569%   $256.1812   $256.18   $256.20   $256.20  
  Purchase #6 $119.92   5.384%   $126.3765   $126.38   $126.40   $126.40  
  Purchase #7 $117.62   4.802%   $123.2681   $123.27   $123.25   $123.30  
  7 purchase totals = $1,116.21       $1,183.6439   $1,183.65   $1,183.65   $1,183.70