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	$55.47	10.201%	$61.1285	$61.13	$61.15	$61.10
Purchase #2	$235.27	5.783%	$248.8757	$248.88	$248.90	$248.90
Purchase #3	$120.87	8.336%	$130.9457	$130.95	$130.95	$130.90
Purchase #4	$203.28	8.331%	$220.2153	$220.22	$220.20	$220.20
Purchase #5	$42.71	10.828%	$47.3346	$47.33	$47.35	$47.30
Purchase #6	$191.66	4.464%	$200.2157	$200.22	$200.20	$200.20
Purchase #7	$170.52	12.326%	$191.5383	$191.54	$191.55	$191.50
7 purchase totals =	$1,019.78		$1,100.2538	$1,100.27	$1,100.30	$1,100.10