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 $79.31   10.812%   $87.885   $87.89   $87.90   $87.90  
  Purchase #2 $90.57   5.679%   $95.7135   $95.71   $95.70   $95.70  
  Purchase #3 $97.49   10.805%   $108.0238   $108.02   $108.00   $108.00  
  Purchase #4 $249.28   5.274%   $262.427   $262.43   $262.45   $262.40  
  Purchase #5 $221.77   10.716%   $245.5349   $245.53   $245.55   $245.50  
  Purchase #6 $179.91   4.367%   $187.7667   $187.77   $187.75   $187.80  
  Purchase #7 $242.86   10.366%   $268.0349   $268.03   $268.05   $268.00  
  7 purchase totals = $1,161.19       $1,255.3858   $1,255.38   $1,255.40   $1,255.30