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	$85.28	5.787%	$90.2152	$90.22	$90.20	$90.20
Purchase #2	$191.74	8.344%	$207.7388	$207.74	$207.75	$207.70
Purchase #3	$221.89	8.314%	$240.3379	$240.34	$240.35	$240.30
Purchase #4	$236.32	13.363%	$267.8994	$267.90	$267.90	$267.90
Purchase #5	$120.92	13.741%	$137.5356	$137.54	$137.55	$137.50
Purchase #6	$178.43	10.124%	$196.4943	$196.49	$196.50	$196.50
Purchase #7	$181.98	8.172%	$196.8514	$196.85	$196.85	$196.90
7 purchase totals =	$1,216.56		$1,337.0726	$1,337.08	$1,337.10	$1,337.00