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	$242.92	12.566%	$273.4453	$273.45	$273.45	$273.40
Purchase #2	$153.54	4.231%	$160.0363	$160.04	$160.05	$160.00
Purchase #3	$217.63	11.191%	$241.985	$241.99	$242.00	$242.00
Purchase #4	$217.93	10.563%	$240.9499	$240.95	$240.95	$240.90
Purchase #5	$131.96	6.309%	$140.2854	$140.29	$140.30	$140.30
Purchase #6	$62.46	7.697%	$67.2675	$67.27	$67.25	$67.30
Purchase #7	$34.86	10.648%	$38.5719	$38.57	$38.55	$38.60
7 purchase totals =	$1,061.30		$1,162.5413	$1,162.56	$1,162.55	$1,162.50