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	$81.53	10.716%	$90.2668	$90.27	$90.25	$90.30
Purchase #2	$93.26	4.305%	$97.2748	$97.27	$97.25	$97.30
Purchase #3	$180.36	6.257%	$191.6451	$191.65	$191.65	$191.60
Purchase #4	$115.37	11.587%	$128.7379	$128.74	$128.75	$128.70
Purchase #5	$179.73	10.402%	$198.4255	$198.43	$198.45	$198.40
Purchase #6	$115.87	3.712%	$120.1711	$120.17	$120.15	$120.20
Purchase #7	$78.42	9.427%	$85.8127	$85.81	$85.80	$85.80
7 purchase totals =	$844.54		$912.3339	$912.34	$912.30	$912.30