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	$166.45	3.562%	$172.3789	$172.38	$172.40	$172.40
Purchase #2	$114.57	5.871%	$121.2964	$121.30	$121.30	$121.30
Purchase #3	$51.42	6.739%	$54.8852	$54.89	$54.90	$54.90
Purchase #4	$222.56	9.319%	$243.3004	$243.30	$243.30	$243.30
Purchase #5	$62.87	9.481%	$68.8307	$68.83	$68.85	$68.80
Purchase #6	$186.31	5.164%	$195.931	$195.93	$195.95	$195.90
Purchase #7	$222.40	9.742%	$244.0662	$244.07	$244.05	$244.10
7 purchase totals =	$1,026.58		$1,100.6888	$1,100.70	$1,100.75	$1,100.70