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	$104.92	4.754%	$109.9079	$109.91	$109.90	$109.90
Purchase #2	$234.57	3.331%	$242.3835	$242.38	$242.40	$242.40
Purchase #3	$46.76	6.755%	$49.9186	$49.92	$49.90	$49.90
Purchase #4	$59.58	11.381%	$66.3608	$66.36	$66.35	$66.40
Purchase #5	$123.83	4.541%	$129.4531	$129.45	$129.45	$129.50
Purchase #6	$191.54	4.613%	$200.3757	$200.38	$200.40	$200.40
Purchase #7	$111.54	10.459%	$123.206	$123.21	$123.20	$123.20
7 purchase totals =	$872.74		$921.6056	$921.61	$921.60	$921.70