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	$159.30	3.640%	$165.0985	$165.10	$165.10	$165.10
Purchase #2	$38.86	12.656%	$43.7781	$43.78	$43.80	$43.80
Purchase #3	$171.78	11.683%	$191.8491	$191.85	$191.85	$191.80
Purchase #4	$179.46	5.812%	$189.8902	$189.89	$189.90	$189.90
Purchase #5	$143.57	10.684%	$158.909	$158.91	$158.90	$158.90
Purchase #6	$5.93	9.251%	$6.4786	$6.48	$6.50	$6.50
Purchase #7	$94.88	4.686%	$99.3261	$99.33	$99.35	$99.30
7 purchase totals =	$793.78		$855.3296	$855.34	$855.40	$855.30