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	$247.25	9.699%	$271.2308	$271.23	$271.25	$271.20
Purchase #2	$221.71	9.538%	$242.8567	$242.86	$242.85	$242.90
Purchase #3	$189.64	4.690%	$198.5341	$198.53	$198.55	$198.50
Purchase #4	$171.47	9.160%	$187.1767	$187.18	$187.20	$187.20
Purchase #5	$155.76	10.333%	$171.8547	$171.85	$171.85	$171.90
Purchase #6	$150.57	3.377%	$155.6547	$155.65	$155.65	$155.70
Purchase #7	$159.69	3.648%	$165.5155	$165.52	$165.50	$165.50
7 purchase totals =	$1,296.09		$1,392.8232	$1,392.82	$1,392.85	$1,392.90