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	$41.27	9.802%	$45.3153	$45.32	$45.30	$45.30
Purchase #2	$120.65	9.348%	$131.9284	$131.93	$131.95	$131.90
Purchase #3	$88.51	12.356%	$99.4463	$99.45	$99.45	$99.40
Purchase #4	$40.28	4.663%	$42.1583	$42.16	$42.15	$42.20
Purchase #5	$104.45	10.764%	$115.693	$115.69	$115.70	$115.70
Purchase #6	$228.28	12.741%	$257.3652	$257.37	$257.35	$257.40
Purchase #7	$89.74	9.457%	$98.2267	$98.23	$98.25	$98.20
7 purchase totals =	$713.18		$790.1332	$790.15	$790.15	$790.10