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	$42.63	6.770%	$45.5161	$45.52	$45.50	$45.50
Purchase #2	$115.46	12.293%	$129.6535	$129.65	$129.65	$129.70
Purchase #3	$235.64	7.531%	$253.386	$253.39	$253.40	$253.40
Purchase #4	$79.41	4.431%	$82.9287	$82.93	$82.95	$82.90
Purchase #5	$80.40	11.326%	$89.5061	$89.51	$89.50	$89.50
Purchase #6	$131.82	7.274%	$141.4086	$141.41	$141.40	$141.40
Purchase #7	$180.30	6.672%	$192.3296	$192.33	$192.35	$192.30
7 purchase totals =	$865.66		$934.7286	$934.74	$934.75	$934.70