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	$177.71	12.815%	$200.4835	$200.48	$200.50	$200.50
Purchase #2	$232.74	6.475%	$247.8099	$247.81	$247.80	$247.80
Purchase #3	$98.61	4.842%	$103.3847	$103.38	$103.40	$103.40
Purchase #4	$64.71	10.524%	$71.5201	$71.52	$71.50	$71.50
Purchase #5	$188.35	12.586%	$212.0557	$212.06	$212.05	$212.10
Purchase #6	$27.26	5.124%	$28.6568	$28.66	$28.65	$28.70
Purchase #7	$29.43	6.129%	$31.2338	$31.23	$31.25	$31.20
7 purchase totals =	$818.81		$895.1445	$895.14	$895.15	$895.20