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	$8.90	11.449%	$9.919	$9.92	$9.90	$9.90
Purchase #2	$58.87	3.726%	$61.0635	$61.06	$61.05	$61.10
Purchase #3	$80.91	12.261%	$90.8304	$90.83	$90.85	$90.80
Purchase #4	$142.26	7.468%	$152.884	$152.88	$152.90	$152.90
Purchase #5	$28.93	4.273%	$30.1662	$30.17	$30.15	$30.20
Purchase #6	$78.49	4.631%	$82.1249	$82.12	$82.10	$82.10
Purchase #7	$180.65	7.425%	$194.0633	$194.06	$194.05	$194.10
7 purchase totals =	$579.01		$621.0513	$621.04	$621.00	$621.10