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	$193.55	12.578%	$217.8947	$217.89	$217.90	$217.90
Purchase #2	$170.86	10.570%	$188.9199	$188.92	$188.90	$188.90
Purchase #3	$184.77	3.669%	$191.5492	$191.55	$191.55	$191.50
Purchase #4	$34.70	3.257%	$35.8302	$35.83	$35.85	$35.80
Purchase #5	$247.28	10.621%	$273.5436	$273.54	$273.55	$273.50
Purchase #6	$162.95	11.216%	$181.2265	$181.23	$181.25	$181.20
Purchase #7	$58.99	12.108%	$66.1325	$66.13	$66.15	$66.10
7 purchase totals =	$1,053.10		$1,155.0966	$1,155.09	$1,155.15	$1,154.90