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	$100.88	8.154%	$109.1058	$109.11	$109.10	$109.10
Purchase #2	$133.50	3.388%	$138.023	$138.02	$138.00	$138.00
Purchase #3	$233.32	7.810%	$251.5423	$251.54	$251.55	$251.50
Purchase #4	$179.62	6.313%	$190.9594	$190.96	$190.95	$191.00
Purchase #5	$30.32	11.646%	$33.8511	$33.85	$33.85	$33.90
Purchase #6	$146.75	13.837%	$167.0558	$167.06	$167.05	$167.10
Purchase #7	$132.63	6.698%	$141.5136	$141.51	$141.50	$141.50
7 purchase totals =	$957.02		$1,032.0510	$1,032.05	$1,032.00	$1,032.10