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	$53.88	10.692%	$59.6408	$59.64	$59.65	$59.60
Purchase #2	$224.78	4.212%	$234.2477	$234.25	$234.25	$234.20
Purchase #3	$98.51	7.275%	$105.6766	$105.68	$105.70	$105.70
Purchase #4	$177.73	12.832%	$200.5363	$200.54	$200.55	$200.50
Purchase #5	$83.98	5.529%	$88.6233	$88.62	$88.60	$88.60
Purchase #6	$57.55	10.516%	$63.602	$63.60	$63.60	$63.60
Purchase #7	$233.78	4.582%	$244.4918	$244.49	$244.50	$244.50
7 purchase totals =	$930.21		$996.8185	$996.82	$996.85	$996.70