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 $158.57   10.746%   $175.6099   $175.61   $175.60   $175.60  
  Purchase #2 $221.99   9.322%   $242.6839   $242.68   $242.70   $242.70  
  Purchase #3 $121.83   11.651%   $136.0244   $136.02   $136.00   $136.00  
  Purchase #4 $223.33   3.768%   $231.7451   $231.75   $231.75   $231.70  
  Purchase #5 $239.71   5.489%   $252.8677   $252.87   $252.85   $252.90  
  Purchase #6 $198.75   9.751%   $218.1301   $218.13   $218.15   $218.10  
  Purchase #7 $149.99   11.528%   $167.2808   $167.28   $167.30   $167.30  
  7 purchase totals = $1,314.17       $1,424.3419   $1,424.34   $1,424.35   $1,424.30