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 $65.85   3.306%   $68.027   $68.03   $68.05   $68.00  
  Purchase #2 $17.38   6.824%   $18.566   $18.57   $18.55   $18.60  
  Purchase #3 $174.26   12.470%   $195.9902   $195.99   $196.00   $196.00  
  Purchase #4 $223.57   10.662%   $247.407   $247.41   $247.40   $247.40  
  Purchase #5 $238.55   6.835%   $254.8549   $254.85   $254.85   $254.90  
  Purchase #6 $225.57   10.791%   $249.9113   $249.91   $249.90   $249.90  
  Purchase #7 $241.42   4.205%   $251.5717   $251.57   $251.55   $251.60  
  7 purchase totals = $1,186.60       $1,286.3281   $1,286.33   $1,286.30   $1,286.40