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	$95.82	3.582%	$99.2523	$99.25	$99.25	$99.30
Purchase #2	$79.84	4.440%	$83.3849	$83.38	$83.40	$83.40
Purchase #3	$78.88	8.348%	$85.4649	$85.46	$85.45	$85.50
Purchase #4	$173.76	4.399%	$181.4037	$181.40	$181.40	$181.40
Purchase #5	$85.64	6.118%	$90.8795	$90.88	$90.90	$90.90
Purchase #6	$111.50	3.362%	$115.2486	$115.25	$115.25	$115.20
Purchase #7	$217.94	7.251%	$233.7428	$233.74	$233.75	$233.70
7 purchase totals =	$843.38		$889.3767	$889.36	$889.40	$889.40