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 $250.42   5.214%   $263.4769   $263.48   $263.50   $263.50  
  Purchase #2 $226.62   8.268%   $245.3569   $245.36   $245.35   $245.40  
  Purchase #3 $214.62   11.467%   $239.2305   $239.23   $239.25   $239.20  
  Purchase #4 $228.86   8.537%   $248.3978   $248.40   $248.40   $248.40  
  Purchase #5 $179.34   12.835%   $202.3583   $202.36   $202.35   $202.40  
  Purchase #6 $31.47   8.644%   $34.1903   $34.19   $34.20   $34.20  
  Purchase #7 $160.33   11.303%   $178.4521   $178.45   $178.45   $178.50  
  7 purchase totals = $1,291.66       $1,411.4628   $1,411.47   $1,411.50   $1,411.60