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	$161.64	9.207%	$176.5222	$176.52	$176.50	$176.50
Purchase #2	$178.58	12.185%	$200.34	$200.34	$200.35	$200.30
Purchase #3	$89.56	10.846%	$99.2737	$99.27	$99.25	$99.30
Purchase #4	$233.32	12.397%	$262.2447	$262.24	$262.25	$262.20
Purchase #5	$97.57	13.362%	$110.6073	$110.61	$110.60	$110.60
Purchase #6	$14.72	3.529%	$15.2395	$15.24	$15.25	$15.20
Purchase #7	$181.57	6.633%	$193.6135	$193.61	$193.60	$193.60
7 purchase totals =	$956.96		$1,057.8409	$1,057.83	$1,057.80	$1,057.70