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 $87.83   9.587%   $96.2503   $96.25   $96.25   $96.30  
  Purchase #2 $114.56   3.164%   $118.1847   $118.18   $118.20   $118.20  
  Purchase #3 $38.42   8.430%   $41.6588   $41.66   $41.65   $41.70  
  Purchase #4 $249.86   7.701%   $269.1017   $269.10   $269.10   $269.10  
  Purchase #5 $16.35   10.513%   $18.0689   $18.07   $18.05   $18.10  
  Purchase #6 $102.48   13.573%   $116.3896   $116.39   $116.40   $116.40  
  Purchase #7 $112.47   9.867%   $123.5674   $123.57   $123.55   $123.60  
  7 purchase totals = $721.97       $783.2214   $783.22   $783.20   $783.40