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	$105.50	10.429%	$116.5026	$116.50	$116.50	$116.50
Purchase #2	$170.40	11.634%	$190.2243	$190.22	$190.20	$190.20
Purchase #3	$180.32	7.379%	$193.6258	$193.63	$193.65	$193.60
Purchase #4	$109.53	6.720%	$116.8904	$116.89	$116.90	$116.90
Purchase #5	$85.63	7.241%	$91.8305	$91.83	$91.85	$91.80
Purchase #6	$42.31	7.414%	$45.4469	$45.45	$45.45	$45.40
Purchase #7	$185.33	7.668%	$199.5411	$199.54	$199.55	$199.50
7 purchase totals =	$879.02		$954.0616	$954.06	$954.10	$953.90