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	$25.27	7.126%	$27.0707	$27.07	$27.05	$27.10
Purchase #2	$130.61	6.585%	$139.2107	$139.21	$139.20	$139.20
Purchase #3	$80.87	13.227%	$91.5667	$91.57	$91.55	$91.60
Purchase #4	$143.83	11.597%	$160.51	$160.51	$160.50	$160.50
Purchase #5	$245.77	13.179%	$278.16	$278.16	$278.15	$278.20
Purchase #6	$71.76	12.502%	$80.7314	$80.73	$80.75	$80.70
Purchase #7	$229.88	10.558%	$254.1507	$254.15	$254.15	$254.20
7 purchase totals =	$927.99		$1,031.4002	$1,031.40	$1,031.35	$1,031.50