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	$29.26	6.412%	$31.1362	$31.14	$31.15	$31.10
Purchase #2	$52.54	13.206%	$59.4784	$59.48	$59.50	$59.50
Purchase #3	$173.84	4.581%	$181.8036	$181.80	$181.80	$181.80
Purchase #4	$242.66	4.610%	$253.8466	$253.85	$253.85	$253.80
Purchase #5	$215.28	13.428%	$244.1878	$244.19	$244.20	$244.20
Purchase #6	$109.28	10.611%	$120.8757	$120.88	$120.90	$120.90
Purchase #7	$103.56	6.137%	$109.9155	$109.92	$109.90	$109.90
7 purchase totals =	$926.42		$1,001.2438	$1,001.26	$1,001.30	$1,001.20