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	$84.46	6.206%	$89.7016	$89.70	$89.70	$89.70
Purchase #2	$195.75	8.292%	$211.9816	$211.98	$212.00	$212.00
Purchase #3	$56.82	13.849%	$64.689	$64.69	$64.70	$64.70
Purchase #4	$197.85	12.418%	$222.419	$222.42	$222.40	$222.40
Purchase #5	$79.48	7.302%	$85.2836	$85.28	$85.30	$85.30
Purchase #6	$159.30	13.779%	$181.2499	$181.25	$181.25	$181.20
Purchase #7	$71.60	9.256%	$78.2273	$78.23	$78.25	$78.20
7 purchase totals =	$845.26		$933.5520	$933.55	$933.60	$933.50