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	$117.83	5.516%	$124.3295	$124.33	$124.35	$124.30
Purchase #2	$89.69	9.620%	$98.3182	$98.32	$98.30	$98.30
Purchase #3	$180.81	9.592%	$198.1533	$198.15	$198.15	$198.20
Purchase #4	$175.83	3.362%	$181.7414	$181.74	$181.75	$181.70
Purchase #5	$144.68	4.465%	$151.14	$151.14	$151.15	$151.10
Purchase #6	$230.39	8.758%	$250.5676	$250.57	$250.55	$250.60
Purchase #7	$189.67	13.650%	$215.56	$215.56	$215.55	$215.60
7 purchase totals =	$1,128.90		$1,219.8100	$1,219.81	$1,219.80	$1,219.80