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	$91.30	13.626%	$103.7405	$103.74	$103.75	$103.70
Purchase #2	$51.67	3.651%	$53.5565	$53.56	$53.55	$53.60
Purchase #3	$170.76	6.529%	$181.9089	$181.91	$181.90	$181.90
Purchase #4	$58.25	12.831%	$65.7241	$65.72	$65.70	$65.70
Purchase #5	$99.92	12.855%	$112.7647	$112.76	$112.75	$112.80
Purchase #6	$220.61	11.160%	$245.2301	$245.23	$245.25	$245.20
Purchase #7	$34.47	12.785%	$38.877	$38.88	$38.90	$38.90
7 purchase totals =	$726.98		$801.8018	$801.80	$801.80	$801.80