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	$143.46	6.207%	$152.3646	$152.36	$152.35	$152.40
Purchase #2	$196.97	13.145%	$222.8617	$222.86	$222.85	$222.90
Purchase #3	$83.28	13.243%	$94.3088	$94.31	$94.30	$94.30
Purchase #4	$194.77	9.592%	$213.4523	$213.45	$213.45	$213.50
Purchase #5	$231.98	11.687%	$259.0915	$259.09	$259.10	$259.10
Purchase #6	$48.26	8.433%	$52.3298	$52.33	$52.35	$52.30
Purchase #7	$89.66	6.766%	$95.7264	$95.73	$95.75	$95.70
7 purchase totals =	$988.38		$1,090.1351	$1,090.13	$1,090.15	$1,090.20