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 $23.77   12.256%   $26.6833   $26.68   $26.70   $26.70  
  Purchase #2 $219.91   9.381%   $240.5398   $240.54   $240.55   $240.50  
  Purchase #3 $91.35   12.449%   $102.7222   $102.72   $102.70   $102.70  
  Purchase #4 $240.28   8.204%   $259.9926   $259.99   $260.00   $260.00  
  Purchase #5 $223.70   12.844%   $252.432   $252.43   $252.45   $252.40  
  Purchase #6 $80.77   3.283%   $83.4217   $83.42   $83.40   $83.40  
  Purchase #7 $188.95   10.470%   $208.7331   $208.73   $208.75   $208.70  
  7 purchase totals = $1,068.73       $1,174.5247   $1,174.51   $1,174.55   $1,174.40