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	$39.79	3.293%	$41.1003	$41.10	$41.10	$41.10
Purchase #2	$63.78	11.499%	$71.1141	$71.11	$71.10	$71.10
Purchase #3	$238.91	11.384%	$266.1075	$266.11	$266.10	$266.10
Purchase #4	$83.47	10.157%	$91.948	$91.95	$91.95	$91.90
Purchase #5	$103.45	7.385%	$111.0898	$111.09	$111.10	$111.10
Purchase #6	$51.56	7.428%	$55.3899	$55.39	$55.40	$55.40
Purchase #7	$160.45	12.751%	$180.909	$180.91	$180.90	$180.90
7 purchase totals =	$741.41		$817.6586	$817.66	$817.65	$817.60