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 $74.77   13.721%   $85.0292   $85.03   $85.05   $85.00  
  Purchase #2 $190.95   11.497%   $212.9035   $212.90   $212.90   $212.90  
  Purchase #3 $218.42   13.444%   $247.7844   $247.78   $247.80   $247.80  
  Purchase #4 $56.89   11.663%   $63.5251   $63.53   $63.55   $63.50  
  Purchase #5 $161.57   10.505%   $178.5429   $178.54   $178.55   $178.50  
  Purchase #6 $188.75   3.686%   $195.7073   $195.71   $195.70   $195.70  
  Purchase #7 $81.29   3.604%   $84.2197   $84.22   $84.20   $84.20  
  7 purchase totals = $972.64       $1,067.7121   $1,067.71   $1,067.75   $1,067.60