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 $82.79   5.779%   $87.5744   $87.57   $87.55   $87.60  
  Purchase #2 $213.40   7.568%   $229.5501   $229.55   $229.55   $229.60  
  Purchase #3 $234.36   5.803%   $247.9599   $247.96   $247.95   $248.00  
  Purchase #4 $46.29   4.636%   $48.436   $48.44   $48.45   $48.40  
  Purchase #5 $28.67   6.565%   $30.5522   $30.55   $30.55   $30.60  
  Purchase #6 $87.66   9.178%   $95.7054   $95.71   $95.70   $95.70  
  Purchase #7 $92.70   3.661%   $96.0937   $96.09   $96.10   $96.10  
  7 purchase totals = $785.87       $835.8717   $835.87   $835.85   $836.00