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	$27.90	3.103%	$28.7657	$28.77	$28.75	$28.80
Purchase #2	$220.33	12.276%	$247.3777	$247.38	$247.40	$247.40
Purchase #3	$242.34	3.807%	$251.5659	$251.57	$251.55	$251.60
Purchase #4	$161.34	8.849%	$175.617	$175.62	$175.60	$175.60
Purchase #5	$84.93	6.230%	$90.2211	$90.22	$90.20	$90.20
Purchase #6	$137.81	10.856%	$152.7707	$152.77	$152.75	$152.80
Purchase #7	$71.25	3.708%	$73.892	$73.89	$73.90	$73.90
7 purchase totals =	$945.90		$1,020.2101	$1,020.22	$1,020.15	$1,020.30