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	$27.88	12.377%	$31.3307	$31.33	$31.35	$31.30
Purchase #2	$121.57	8.476%	$131.8743	$131.87	$131.85	$131.90
Purchase #3	$157.74	11.412%	$175.7413	$175.74	$175.75	$175.70
Purchase #4	$67.60	4.672%	$70.7583	$70.76	$70.75	$70.80
Purchase #5	$171.60	12.721%	$193.4292	$193.43	$193.45	$193.40
Purchase #6	$144.66	5.483%	$152.5917	$152.59	$152.60	$152.60
Purchase #7	$134.60	10.393%	$148.589	$148.59	$148.60	$148.60
7 purchase totals =	$825.65		$904.3145	$904.31	$904.35	$904.30