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 $54.73   7.448%   $58.8063   $58.81   $58.80   $58.80  
  Purchase #2 $194.57   5.836%   $205.9251   $205.93   $205.95   $205.90  
  Purchase #3 $31.31   6.161%   $33.239   $33.24   $33.25   $33.20  
  Purchase #4 $223.84   6.276%   $237.8882   $237.89   $237.90   $237.90  
  Purchase #5 $188.89   13.658%   $214.6886   $214.69   $214.70   $214.70  
  Purchase #6 $184.79   9.306%   $201.9866   $201.99   $202.00   $202.00  
  Purchase #7 $151.61   4.503%   $158.437   $158.44   $158.45   $158.40  
  7 purchase totals = $1,029.74       $1,110.9708   $1,110.99   $1,111.05   $1,110.90