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 $93.64   11.142%   $104.0734   $104.07   $104.05   $104.10  
  Purchase #2 $112.84   4.225%   $117.6075   $117.61   $117.60   $117.60  
  Purchase #3 $241.30   6.614%   $257.2596   $257.26   $257.25   $257.30  
  Purchase #4 $54.87   4.505%   $57.3419   $57.34   $57.35   $57.30  
  Purchase #5 $175.26   7.261%   $187.9856   $187.99   $188.00   $188.00  
  Purchase #6 $249.70   11.715%   $278.9524   $278.95   $278.95   $279.00  
  Purchase #7 $239.61   7.823%   $258.3547   $258.35   $258.35   $258.40  
  7 purchase totals = $1,167.22       $1,261.5751   $1,261.57   $1,261.55   $1,261.70