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	$20.70	4.312%	$21.5926	$21.59	$21.60	$21.60
Purchase #2	$151.85	6.327%	$161.4575	$161.46	$161.45	$161.50
Purchase #3	$61.30	10.772%	$67.9032	$67.90	$67.90	$67.90
Purchase #4	$161.60	6.131%	$171.5077	$171.51	$171.50	$171.50
Purchase #5	$82.57	10.703%	$91.4075	$91.41	$91.40	$91.40
Purchase #6	$5.77	10.297%	$6.3641	$6.36	$6.35	$6.40
Purchase #7	$5.72	8.132%	$6.1852	$6.19	$6.20	$6.20
7 purchase totals =	$489.51		$526.4178	$526.42	$526.40	$526.50