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	$156.74	6.109%	$166.3152	$166.32	$166.30	$166.30
Purchase #2	$83.69	12.436%	$94.0977	$94.10	$94.10	$94.10
Purchase #3	$239.94	13.826%	$273.1141	$273.11	$273.10	$273.10
Purchase #4	$41.51	10.444%	$45.8453	$45.85	$45.85	$45.80
Purchase #5	$177.60	12.530%	$199.8533	$199.85	$199.85	$199.90
Purchase #6	$42.90	5.726%	$45.3565	$45.36	$45.35	$45.40
Purchase #7	$109.25	4.717%	$114.4033	$114.40	$114.40	$114.40
7 purchase totals =	$851.63		$938.9854	$938.99	$938.95	$939.00