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 $241.35   8.311%   $261.4086   $261.41   $261.40   $261.40  
  Purchase #2 $167.63   6.385%   $178.3332   $178.33   $178.35   $178.30  
  Purchase #3 $147.29   6.220%   $156.4514   $156.45   $156.45   $156.50  
  Purchase #4 $180.67   10.286%   $199.2537   $199.25   $199.25   $199.30  
  Purchase #5 $72.94   12.365%   $81.959   $81.96   $81.95   $82.00  
  Purchase #6 $14.69   6.120%   $15.589   $15.59   $15.60   $15.60  
  Purchase #7 $246.65   5.175%   $259.4141   $259.41   $259.40   $259.40  
  7 purchase totals = $1,071.22       $1,152.4090   $1,152.40   $1,152.40   $1,152.50