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 $243.39   13.402%   $276.0091   $276.01   $276.00   $276.00  
  Purchase #2 $141.68   7.110%   $151.7534   $151.75   $151.75   $151.80  
  Purchase #3 $119.99   7.138%   $128.5549   $128.55   $128.55   $128.60  
  Purchase #4 $65.51   13.112%   $74.0997   $74.10   $74.10   $74.10  
  Purchase #5 $120.46   4.109%   $125.4097   $125.41   $125.40   $125.40  
  Purchase #6 $213.92   5.688%   $226.0878   $226.09   $226.10   $226.10  
  Purchase #7 $120.37   8.132%   $130.1585   $130.16   $130.15   $130.20  
  7 purchase totals = $1,025.32       $1,112.0731   $1,112.07   $1,112.05   $1,112.20