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	$161.78	12.171%	$181.4702	$181.47	$181.45	$181.50
Purchase #2	$166.43	3.275%	$171.8806	$171.88	$171.90	$171.90
Purchase #3	$16.96	5.351%	$17.8675	$17.87	$17.85	$17.90
Purchase #4	$55.71	7.421%	$59.8442	$59.84	$59.85	$59.80
Purchase #5	$83.69	3.250%	$86.4099	$86.41	$86.40	$86.40
Purchase #6	$49.33	12.593%	$55.5421	$55.54	$55.55	$55.50
Purchase #7	$61.91	5.774%	$65.4847	$65.48	$65.50	$65.50
7 purchase totals =	$595.81		$638.4992	$638.49	$638.50	$638.50