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	$123.54	6.488%	$131.5553	$131.56	$131.55	$131.60
Purchase #2	$40.56	11.711%	$45.31	$45.31	$45.30	$45.30
Purchase #3	$75.34	10.125%	$82.9682	$82.97	$82.95	$83.00
Purchase #4	$26.61	4.208%	$27.7297	$27.73	$27.75	$27.70
Purchase #5	$249.75	6.132%	$265.0647	$265.06	$265.05	$265.10
Purchase #6	$178.38	9.668%	$195.6258	$195.63	$195.65	$195.60
Purchase #7	$198.34	3.147%	$204.5818	$204.58	$204.60	$204.60
7 purchase totals =	$892.52		$952.8355	$952.84	$952.85	$952.90