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 $88.72   13.861%   $101.0175   $101.02   $101.00   $101.00  
  Purchase #2 $195.50   4.128%   $203.5702   $203.57   $203.55   $203.60  
  Purchase #3 $217.32   7.866%   $234.4144   $234.41   $234.40   $234.40  
  Purchase #4 $136.79   12.126%   $153.3772   $153.38   $153.40   $153.40  
  Purchase #5 $187.77   5.208%   $197.5491   $197.55   $197.55   $197.50  
  Purchase #6 $242.29   13.486%   $274.9652   $274.97   $274.95   $275.00  
  Purchase #7 $148.27   11.747%   $165.6873   $165.69   $165.70   $165.70  
  7 purchase totals = $1,216.66       $1,330.5809   $1,330.59   $1,330.55   $1,330.60