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	$52.73	9.253%	$57.6091	$57.61	$57.60	$57.60
Purchase #2	$175.88	11.725%	$196.5019	$196.50	$196.50	$196.50
Purchase #3	$224.47	11.780%	$250.9126	$250.91	$250.90	$250.90
Purchase #4	$222.25	8.313%	$240.7256	$240.73	$240.75	$240.70
Purchase #5	$248.67	4.526%	$259.9248	$259.92	$259.90	$259.90
Purchase #6	$166.50	13.166%	$188.4214	$188.42	$188.40	$188.40
Purchase #7	$96.28	13.334%	$109.118	$109.12	$109.10	$109.10
7 purchase totals =	$1,186.78		$1,303.2134	$1,303.21	$1,303.15	$1,303.10