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 $214.97   3.243%   $221.9415   $221.94   $221.95   $221.90  
  Purchase #2 $130.37   5.758%   $137.8767   $137.88   $137.90   $137.90  
  Purchase #3 $117.43   6.288%   $124.814   $124.81   $124.80   $124.80  
  Purchase #4 $107.37   6.169%   $113.9937   $113.99   $114.00   $114.00  
  Purchase #5 $54.59   5.592%   $57.6427   $57.64   $57.65   $57.60  
  Purchase #6 $244.83   9.134%   $267.1928   $267.19   $267.20   $267.20  
  Purchase #7 $168.55   3.350%   $174.1964   $174.20   $174.20   $174.20  
  7 purchase totals = $1,038.11       $1,097.6578   $1,097.65   $1,097.70   $1,097.60