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	$127.64	10.734%	$141.3409	$141.34	$141.35	$141.30
Purchase #2	$164.92	12.578%	$185.6636	$185.66	$185.65	$185.70
Purchase #3	$93.82	5.517%	$98.996	$99.00	$99.00	$99.00
Purchase #4	$83.95	7.492%	$90.2395	$90.24	$90.25	$90.20
Purchase #5	$82.58	11.222%	$91.8471	$91.85	$91.85	$91.80
Purchase #6	$205.62	9.282%	$224.7056	$224.71	$224.70	$224.70
Purchase #7	$52.30	6.400%	$55.6472	$55.65	$55.65	$55.60
7 purchase totals =	$810.83		$888.4399	$888.45	$888.45	$888.30