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	$51.89	5.508%	$54.7481	$54.75	$54.75	$54.70
Purchase #2	$35.94	5.494%	$37.9145	$37.91	$37.90	$37.90
Purchase #3	$190.92	9.541%	$209.1357	$209.14	$209.15	$209.10
Purchase #4	$70.54	3.335%	$72.8925	$72.89	$72.90	$72.90
Purchase #5	$99.63	6.390%	$105.9964	$106.00	$106.00	$106.00
Purchase #6	$35.37	8.810%	$38.4861	$38.49	$38.50	$38.50
Purchase #7	$143.36	3.862%	$148.8966	$148.90	$148.90	$148.90
7 purchase totals =	$627.65		$668.0699	$668.08	$668.10	$668.00