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 $187.68   10.627%   $207.6248   $207.62   $207.60   $207.60  
  Purchase #2 $245.79   12.522%   $276.5678   $276.57   $276.55   $276.60  
  Purchase #3 $202.99   5.832%   $214.8284   $214.83   $214.85   $214.80  
  Purchase #4 $184.53   5.295%   $194.3009   $194.30   $194.30   $194.30  
  Purchase #5 $41.75   12.206%   $46.846   $46.85   $46.85   $46.80  
  Purchase #6 $131.56   4.387%   $137.3315   $137.33   $137.35   $137.30  
  Purchase #7 $213.69   5.463%   $225.3639   $225.36   $225.35   $225.40  
  7 purchase totals = $1,207.99       $1,302.8633   $1,302.86   $1,302.85   $1,302.80