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	$91.94	8.344%	$99.6115	$99.61	$99.60	$99.60
Purchase #2	$244.61	9.597%	$268.0852	$268.09	$268.10	$268.10
Purchase #3	$47.89	13.585%	$54.3959	$54.40	$54.40	$54.40
Purchase #4	$206.30	11.191%	$229.387	$229.39	$229.40	$229.40
Purchase #5	$29.59	8.833%	$32.2037	$32.20	$32.20	$32.20
Purchase #6	$62.56	10.804%	$69.319	$69.32	$69.30	$69.30
Purchase #7	$170.50	4.725%	$178.5561	$178.56	$178.55	$178.60
7 purchase totals =	$853.39		$931.5584	$931.57	$931.55	$931.60