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 $241.78   10.274%   $266.6205   $266.62   $266.60   $266.60  
  Purchase #2 $117.49   12.682%   $132.3901   $132.39   $132.40   $132.40  
  Purchase #3 $198.77   10.524%   $219.6886   $219.69   $219.70   $219.70  
  Purchase #4 $54.96   4.346%   $57.3486   $57.35   $57.35   $57.30  
  Purchase #5 $137.31   8.804%   $149.3988   $149.40   $149.40   $149.40  
  Purchase #6 $159.99   11.242%   $177.9761   $177.98   $178.00   $178.00  
  Purchase #7 $23.75   3.440%   $24.567   $24.57   $24.55   $24.60  
  7 purchase totals = $934.05       $1,027.9897   $1,028.00   $1,028.00   $1,028.00