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 $192.35   5.511%   $202.9504   $202.95   $202.95   $203.00  
  Purchase #2 $41.50   8.246%   $44.9221   $44.92   $44.90   $44.90  
  Purchase #3 $187.34   5.811%   $198.2263   $198.23   $198.25   $198.20  
  Purchase #4 $207.58   7.564%   $223.2814   $223.28   $223.30   $223.30  
  Purchase #5 $142.93   13.343%   $162.0011   $162.00   $162.00   $162.00  
  Purchase #6 $115.38   3.805%   $119.7702   $119.77   $119.75   $119.80  
  Purchase #7 $214.26   6.557%   $228.309   $228.31   $228.30   $228.30  
  7 purchase totals = $1,101.34       $1,179.4605   $1,179.46   $1,179.45   $1,179.50