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	$82.42	11.742%	$92.0978	$92.10	$92.10	$92.10
Purchase #2	$47.37	12.714%	$53.3926	$53.39	$53.40	$53.40
Purchase #3	$194.40	9.780%	$213.4123	$213.41	$213.40	$213.40
Purchase #4	$178.77	9.298%	$195.392	$195.39	$195.40	$195.40
Purchase #5	$91.28	13.408%	$103.5188	$103.52	$103.50	$103.50
Purchase #6	$225.33	4.119%	$234.6113	$234.61	$234.60	$234.60
Purchase #7	$27.46	3.701%	$28.4763	$28.48	$28.50	$28.50
7 purchase totals =	$847.03		$920.9011	$920.90	$920.90	$920.90