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	$80.29	3.828%	$83.3635	$83.36	$83.35	$83.40
Purchase #2	$211.45	12.736%	$238.3803	$238.38	$238.40	$238.40
Purchase #3	$168.52	8.365%	$182.6167	$182.62	$182.60	$182.60
Purchase #4	$71.90	7.779%	$77.4931	$77.49	$77.50	$77.50
Purchase #5	$189.33	3.292%	$195.5627	$195.56	$195.55	$195.60
Purchase #6	$244.50	4.222%	$254.8228	$254.82	$254.80	$254.80
Purchase #7	$206.77	11.503%	$230.5548	$230.55	$230.55	$230.60
7 purchase totals =	$1,172.76		$1,262.7939	$1,262.78	$1,262.75	$1,262.90