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 $101.80   11.771%   $113.7829   $113.78   $113.80   $113.80  
  Purchase #2 $11.92   6.429%   $12.6863   $12.69   $12.70   $12.70  
  Purchase #3 $226.84   9.784%   $249.034   $249.03   $249.05   $249.00  
  Purchase #4 $103.91   3.383%   $107.4253   $107.43   $107.45   $107.40  
  Purchase #5 $246.81   5.627%   $260.698   $260.70   $260.70   $260.70  
  Purchase #6 $178.32   4.167%   $185.7506   $185.75   $185.75   $185.80  
  Purchase #7 $128.57   4.417%   $134.2489   $134.25   $134.25   $134.20  
  7 purchase totals = $998.17       $1,063.6260   $1,063.63   $1,063.70   $1,063.60