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 $245.56   8.342%   $266.0446   $266.04   $266.05   $266.00  
  Purchase #2 $208.70   11.519%   $232.7402   $232.74   $232.75   $232.70  
  Purchase #3 $81.33   6.470%   $86.5921   $86.59   $86.60   $86.60  
  Purchase #4 $126.63   9.342%   $138.4598   $138.46   $138.45   $138.50  
  Purchase #5 $86.83   4.559%   $90.7886   $90.79   $90.80   $90.80  
  Purchase #6 $160.54   8.629%   $174.393   $174.39   $174.40   $174.40  
  Purchase #7 $220.65   9.848%   $242.3796   $242.38   $242.40   $242.40  
  7 purchase totals = $1,130.24       $1,231.3979   $1,231.39   $1,231.45   $1,231.40