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 $84.73   12.462%   $95.2891   $95.29   $95.30   $95.30  
  Purchase #2 $110.74   11.223%   $123.1684   $123.17   $123.15   $123.20  
  Purchase #3 $140.77   8.390%   $152.5806   $152.58   $152.60   $152.60  
  Purchase #4 $242.42   9.144%   $264.5869   $264.59   $264.60   $264.60  
  Purchase #5 $212.74   6.845%   $227.3021   $227.30   $227.30   $227.30  
  Purchase #6 $60.79   5.371%   $64.055   $64.06   $64.05   $64.10  
  Purchase #7 $122.26   12.186%   $137.1586   $137.16   $137.15   $137.20  
  7 purchase totals = $974.45       $1,064.1407   $1,064.15   $1,064.15   $1,064.30