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 $127.39   5.314%   $134.1595   $134.16   $134.15   $134.20  
  Purchase #2 $223.65   4.593%   $233.9222   $233.92   $233.90   $233.90  
  Purchase #3 $60.38   5.751%   $63.8525   $63.85   $63.85   $63.90  
  Purchase #4 $209.97   10.256%   $231.5045   $231.50   $231.50   $231.50  
  Purchase #5 $96.67   4.715%   $101.228   $101.23   $101.25   $101.20  
  Purchase #6 $83.93   5.222%   $88.3128   $88.31   $88.30   $88.30  
  Purchase #7 $247.64   6.134%   $262.8302   $262.83   $262.85   $262.80  
  7 purchase totals = $1,049.63       $1,115.8097   $1,115.80   $1,115.80   $1,115.80