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	$18.86	7.183%	$20.2147	$20.21	$20.20	$20.20
Purchase #2	$203.73	10.816%	$225.7654	$225.77	$225.75	$225.80
Purchase #3	$104.61	5.585%	$110.4525	$110.45	$110.45	$110.50
Purchase #4	$200.59	10.546%	$221.7442	$221.74	$221.75	$221.70
Purchase #5	$42.77	9.532%	$46.8468	$46.85	$46.85	$46.80
Purchase #6	$105.69	8.490%	$114.6631	$114.66	$114.65	$114.70
Purchase #7	$97.29	8.186%	$105.2542	$105.25	$105.25	$105.30
7 purchase totals =	$773.54		$844.9409	$844.93	$844.90	$845.00