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	$244.51	11.150%	$271.7729	$271.77	$271.75	$271.80
Purchase #2	$129.57	12.292%	$145.4967	$145.50	$145.50	$145.50
Purchase #3	$247.48	9.261%	$270.3991	$270.40	$270.40	$270.40
Purchase #4	$156.50	7.506%	$168.2469	$168.25	$168.25	$168.20
Purchase #5	$188.82	10.568%	$208.7745	$208.77	$208.75	$208.80
Purchase #6	$93.52	11.535%	$104.3075	$104.31	$104.30	$104.30
Purchase #7	$35.84	13.138%	$40.5487	$40.55	$40.55	$40.50
7 purchase totals =	$1,096.24		$1,209.5463	$1,209.55	$1,209.50	$1,209.50