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	$121.52	13.142%	$137.4902	$137.49	$137.50	$137.50
Purchase #2	$190.69	5.169%	$200.5468	$200.55	$200.55	$200.50
Purchase #3	$117.91	9.110%	$128.6516	$128.65	$128.65	$128.70
Purchase #4	$165.34	12.454%	$185.9314	$185.93	$185.95	$185.90
Purchase #5	$211.74	13.709%	$240.7674	$240.77	$240.75	$240.80
Purchase #6	$189.56	3.355%	$195.9197	$195.92	$195.90	$195.90
Purchase #7	$62.47	6.321%	$66.4187	$66.42	$66.40	$66.40
7 purchase totals =	$1,059.23		$1,155.7258	$1,155.73	$1,155.70	$1,155.70