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	$33.49	6.827%	$35.7764	$35.78	$35.80	$35.80
Purchase #2	$79.27	5.525%	$83.6497	$83.65	$83.65	$83.60
Purchase #3	$184.98	13.767%	$210.4462	$210.45	$210.45	$210.40
Purchase #4	$106.61	12.377%	$119.8051	$119.81	$119.80	$119.80
Purchase #5	$82.82	7.782%	$89.2651	$89.27	$89.25	$89.30
Purchase #6	$89.66	8.660%	$97.4246	$97.42	$97.40	$97.40
Purchase #7	$217.44	12.236%	$244.046	$244.05	$244.05	$244.00
7 purchase totals =	$794.27		$880.4131	$880.43	$880.40	$880.30