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 $207.69   9.670%   $227.7736   $227.77   $227.75   $227.80  
  Purchase #2 $51.98   5.194%   $54.6798   $54.68   $54.70   $54.70  
  Purchase #3 $175.49   13.237%   $198.7196   $198.72   $198.70   $198.70  
  Purchase #4 $89.61   10.824%   $99.3094   $99.31   $99.30   $99.30  
  Purchase #5 $191.70   13.828%   $218.2083   $218.21   $218.20   $218.20  
  Purchase #6 $201.88   12.641%   $227.3997   $227.40   $227.40   $227.40  
  Purchase #7 $200.25   13.145%   $226.5729   $226.57   $226.55   $226.60  
  7 purchase totals = $1,118.60       $1,252.6633   $1,252.66   $1,252.60   $1,252.70