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	$85.35	4.592%	$89.2693	$89.27	$89.25	$89.30
Purchase #2	$144.51	8.274%	$156.4668	$156.47	$156.45	$156.50
Purchase #3	$12.76	9.111%	$13.9226	$13.92	$13.90	$13.90
Purchase #4	$156.47	9.558%	$171.4254	$171.43	$171.45	$171.40
Purchase #5	$215.86	3.523%	$223.4647	$223.46	$223.45	$223.50
Purchase #6	$91.57	6.180%	$97.229	$97.23	$97.25	$97.20
Purchase #7	$30.99	5.852%	$32.8035	$32.80	$32.80	$32.80
7 purchase totals =	$737.51		$784.5813	$784.58	$784.55	$784.60