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	$38.50	10.240%	$42.4424	$42.44	$42.45	$42.40
Purchase #2	$38.34	7.830%	$41.342	$41.34	$41.35	$41.30
Purchase #3	$72.60	8.340%	$78.6548	$78.65	$78.65	$78.70
Purchase #4	$225.86	8.199%	$244.3783	$244.38	$244.40	$244.40
Purchase #5	$139.80	6.503%	$148.8912	$148.89	$148.90	$148.90
Purchase #6	$179.64	6.194%	$190.7669	$190.77	$190.75	$190.80
Purchase #7	$247.25	7.150%	$264.9284	$264.93	$264.95	$264.90
7 purchase totals =	$941.99		$1,011.4040	$1,011.40	$1,011.45	$1,011.40