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 $233.85   12.463%   $262.9947   $262.99   $263.00   $263.00  
  Purchase #2 $169.93   7.790%   $183.1675   $183.17   $183.15   $183.20  
  Purchase #3 $32.61   3.560%   $33.7709   $33.77   $33.75   $33.80  
  Purchase #4 $195.47   3.654%   $202.6125   $202.61   $202.60   $202.60  
  Purchase #5 $78.41   4.282%   $81.7675   $81.77   $81.75   $81.80  
  Purchase #6 $162.92   10.762%   $180.4535   $180.45   $180.45   $180.50  
  Purchase #7 $80.93   7.423%   $86.9374   $86.94   $86.95   $86.90  
  7 purchase totals = $954.12       $1,031.7040   $1,031.70   $1,031.65   $1,031.80