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 $248.73   11.273%   $276.7693   $276.77   $276.75   $276.80  
  Purchase #2 $56.43   6.360%   $60.0189   $60.02   $60.00   $60.00  
  Purchase #3 $168.54   9.714%   $184.912   $184.91   $184.90   $184.90  
  Purchase #4 $164.64   11.191%   $183.0649   $183.06   $183.05   $183.10  
  Purchase #5 $138.65   13.254%   $157.0267   $157.03   $157.05   $157.00  
  Purchase #6 $186.90   5.140%   $196.5067   $196.51   $196.50   $196.50  
  Purchase #7 $187.64   8.349%   $203.3061   $203.31   $203.30   $203.30  
  7 purchase totals = $1,151.53       $1,261.6046   $1,261.61   $1,261.55   $1,261.60