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	$38.78	12.418%	$43.5957	$43.60	$43.60	$43.60
Purchase #2	$99.84	10.637%	$110.46	$110.46	$110.45	$110.50
Purchase #3	$100.31	13.266%	$113.6171	$113.62	$113.60	$113.60
Purchase #4	$28.34	4.873%	$29.721	$29.72	$29.70	$29.70
Purchase #5	$248.81	6.216%	$264.276	$264.28	$264.30	$264.30
Purchase #6	$77.46	4.487%	$80.9356	$80.94	$80.95	$80.90
Purchase #7	$78.76	12.811%	$88.8499	$88.85	$88.85	$88.80
7 purchase totals =	$672.30		$731.4553	$731.47	$731.45	$731.40