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 $249.67   11.619%   $278.6792   $278.68   $278.70   $278.70  
  Purchase #2 $212.41   5.152%   $223.3534   $223.35   $223.35   $223.40  
  Purchase #3 $49.47   8.681%   $53.7645   $53.76   $53.75   $53.80  
  Purchase #4 $84.94   9.762%   $93.2318   $93.23   $93.25   $93.20  
  Purchase #5 $245.43   3.661%   $254.4152   $254.42   $254.40   $254.40  
  Purchase #6 $187.90   9.396%   $205.5551   $205.56   $205.55   $205.60  
  Purchase #7 $242.56   6.366%   $258.0014   $258.00   $258.00   $258.00  
  7 purchase totals = $1,272.38       $1,367.0006   $1,367.00   $1,367.00   $1,367.10