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	$95.26	5.315%	$100.3231	$100.32	$100.30	$100.30
Purchase #2	$62.96	13.372%	$71.379	$71.38	$71.40	$71.40
Purchase #3	$92.51	5.303%	$97.4158	$97.42	$97.40	$97.40
Purchase #4	$80.95	10.608%	$89.5372	$89.54	$89.55	$89.50
Purchase #5	$93.66	9.776%	$102.8162	$102.82	$102.80	$102.80
Purchase #6	$165.40	5.325%	$174.2076	$174.21	$174.20	$174.20
Purchase #7	$68.43	3.343%	$70.7176	$70.72	$70.70	$70.70
7 purchase totals =	$659.17		$706.3965	$706.41	$706.35	$706.30