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	$242.72	12.542%	$273.1619	$273.16	$273.15	$273.20
Purchase #2	$242.46	11.532%	$270.4205	$270.42	$270.40	$270.40
Purchase #3	$123.90	12.552%	$139.4519	$139.45	$139.45	$139.50
Purchase #4	$181.48	6.626%	$193.5049	$193.50	$193.50	$193.50
Purchase #5	$214.60	13.528%	$243.6311	$243.63	$243.65	$243.60
Purchase #6	$225.83	12.304%	$253.6161	$253.62	$253.60	$253.60
Purchase #7	$182.85	7.546%	$196.6479	$196.65	$196.65	$196.60
7 purchase totals =	$1,413.84		$1,570.4343	$1,570.43	$1,570.40	$1,570.40