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 $220.48   11.127%   $245.0128   $245.01   $245.00   $245.00  
  Purchase #2 $238.99   12.304%   $268.3953   $268.40   $268.40   $268.40  
  Purchase #3 $56.73   12.626%   $63.8927   $63.89   $63.90   $63.90  
  Purchase #4 $68.58   5.395%   $72.2799   $72.28   $72.30   $72.30  
  Purchase #5 $244.26   10.528%   $269.9757   $269.98   $270.00   $270.00  
  Purchase #6 $177.73   11.662%   $198.4569   $198.46   $198.45   $198.50  
  Purchase #7 $227.53   10.203%   $250.7449   $250.74   $250.75   $250.70  
  7 purchase totals = $1,234.30       $1,368.7582   $1,368.76   $1,368.80   $1,368.80