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	$48.28	7.415%	$51.86	$51.86	$51.85	$51.90
Purchase #2	$168.64	3.556%	$174.6368	$174.64	$174.65	$174.60
Purchase #3	$35.84	13.788%	$40.7816	$40.78	$40.80	$40.80
Purchase #4	$47.69	8.711%	$51.8443	$51.84	$51.85	$51.80
Purchase #5	$221.88	10.356%	$244.8579	$244.86	$244.85	$244.90
Purchase #6	$244.32	6.506%	$260.2155	$260.22	$260.20	$260.20
Purchase #7	$243.89	4.818%	$255.6406	$255.64	$255.65	$255.60
7 purchase totals =	$1,010.54		$1,079.8367	$1,079.84	$1,079.85	$1,079.80