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 $23.90   11.199%   $26.5766   $26.58   $26.60   $26.60  
  Purchase #2 $232.45   5.799%   $245.9298   $245.93   $245.95   $245.90  
  Purchase #3 $85.68   10.122%   $94.3525   $94.35   $94.35   $94.40  
  Purchase #4 $59.28   12.842%   $66.8927   $66.89   $66.90   $66.90  
  Purchase #5 $131.48   12.194%   $147.5127   $147.51   $147.50   $147.50  
  Purchase #6 $168.92   13.189%   $191.1989   $191.20   $191.20   $191.20  
  Purchase #7 $136.61   6.869%   $145.9937   $145.99   $146.00   $146.00  
  7 purchase totals = $838.32       $918.4569   $918.45   $918.50   $918.50