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	$103.30	5.269%	$108.7429	$108.74	$108.75	$108.70
Purchase #2	$242.78	13.636%	$275.8855	$275.89	$275.90	$275.90
Purchase #3	$132.68	11.557%	$148.0138	$148.01	$148.00	$148.00
Purchase #4	$49.51	11.129%	$55.02	$55.02	$55.00	$55.00
Purchase #5	$211.56	6.760%	$225.8615	$225.86	$225.85	$225.90
Purchase #6	$31.90	12.771%	$35.9739	$35.97	$35.95	$36.00
Purchase #7	$148.92	13.831%	$169.5171	$169.52	$169.50	$169.50
7 purchase totals =	$920.65		$1,019.0147	$1,019.01	$1,018.95	$1,019.00