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	$110.99	12.179%	$124.5075	$124.51	$124.50	$124.50
Purchase #2	$224.77	6.842%	$240.1488	$240.15	$240.15	$240.10
Purchase #3	$79.29	12.553%	$89.2433	$89.24	$89.25	$89.20
Purchase #4	$131.32	3.222%	$135.5511	$135.55	$135.55	$135.60
Purchase #5	$139.73	11.837%	$156.2698	$156.27	$156.25	$156.30
Purchase #6	$158.85	4.764%	$166.4176	$166.42	$166.40	$166.40
Purchase #7	$174.77	3.756%	$181.3344	$181.33	$181.35	$181.30
7 purchase totals =	$1,019.72		$1,093.4725	$1,093.47	$1,093.45	$1,093.40