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 $190.25   6.711%   $203.0177   $203.02   $203.00   $203.00  
  Purchase #2 $248.55   11.631%   $277.4589   $277.46   $277.45   $277.50  
  Purchase #3 $172.93   8.452%   $187.546   $187.55   $187.55   $187.50  
  Purchase #4 $15.47   11.549%   $17.2566   $17.26   $17.25   $17.30  
  Purchase #5 $223.58   9.739%   $245.3545   $245.35   $245.35   $245.40  
  Purchase #6 $32.41   6.117%   $34.3925   $34.39   $34.40   $34.40  
  Purchase #7 $142.82   3.110%   $147.2617   $147.26   $147.25   $147.30  
  7 purchase totals = $1,026.01       $1,112.2879   $1,112.29   $1,112.25   $1,112.40