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 $203.96   4.725%   $213.5971   $213.60   $213.60   $213.60  
  Purchase #2 $13.57   5.366%   $14.2982   $14.30   $14.30   $14.30  
  Purchase #3 $181.61   4.436%   $189.6662   $189.67   $189.65   $189.70  
  Purchase #4 $217.70   8.327%   $235.8279   $235.83   $235.85   $235.80  
  Purchase #5 $69.29   13.552%   $78.6802   $78.68   $78.70   $78.70  
  Purchase #6 $225.59   11.477%   $251.481   $251.48   $251.50   $251.50  
  Purchase #7 $217.46   10.255%   $239.7605   $239.76   $239.75   $239.80  
  7 purchase totals = $1,129.18       $1,223.3111   $1,223.32   $1,223.35   $1,223.40