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 $229.69   9.509%   $251.5312   $251.53   $251.55   $251.50  
  Purchase #2 $21.25   8.607%   $23.079   $23.08   $23.10   $23.10  
  Purchase #3 $244.68   10.171%   $269.5664   $269.57   $269.55   $269.60  
  Purchase #4 $32.49   7.507%   $34.929   $34.93   $34.95   $34.90  
  Purchase #5 $228.73   9.663%   $250.8322   $250.83   $250.85   $250.80  
  Purchase #6 $84.28   10.349%   $93.0021   $93.00   $93.00   $93.00  
  Purchase #7 $182.71   8.782%   $198.7556   $198.76   $198.75   $198.80  
  7 purchase totals = $1,023.83       $1,121.6955   $1,121.70   $1,121.75   $1,121.70