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 $241.93   8.435%   $262.3368   $262.34   $262.35   $262.30  
  Purchase #2 $155.79   13.399%   $176.6643   $176.66   $176.65   $176.70  
  Purchase #3 $114.48   6.134%   $121.5022   $121.50   $121.50   $121.50  
  Purchase #4 $60.84   10.626%   $67.3049   $67.30   $67.30   $67.30  
  Purchase #5 $111.61   5.601%   $117.8613   $117.86   $117.85   $117.90  
  Purchase #6 $190.80   13.642%   $216.8289   $216.83   $216.85   $216.80  
  Purchase #7 $178.58   8.557%   $193.8611   $193.86   $193.85   $193.90  
  7 purchase totals = $1,054.03       $1,156.3595   $1,156.35   $1,156.35   $1,156.40