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	$30.98	4.588%	$32.4014	$32.40	$32.40	$32.40
Purchase #2	$158.55	12.342%	$178.1182	$178.12	$178.10	$178.10
Purchase #3	$250.37	7.664%	$269.5584	$269.56	$269.55	$269.60
Purchase #4	$209.61	8.123%	$226.6366	$226.64	$226.65	$226.60
Purchase #5	$41.99	12.740%	$47.3395	$47.34	$47.35	$47.30
Purchase #6	$139.86	11.230%	$155.5663	$155.57	$155.55	$155.60
Purchase #7	$88.35	12.345%	$99.2568	$99.26	$99.25	$99.30
7 purchase totals =	$919.71		$1,008.8772	$1,008.89	$1,008.85	$1,008.90