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	$6.69	10.544%	$7.3954	$7.40	$7.40	$7.40
Purchase #2	$52.65	5.174%	$55.3741	$55.37	$55.35	$55.40
Purchase #3	$247.80	9.628%	$271.6582	$271.66	$271.65	$271.70
Purchase #4	$49.34	3.184%	$50.911	$50.91	$50.90	$50.90
Purchase #5	$131.63	6.217%	$139.8134	$139.81	$139.80	$139.80
Purchase #6	$243.37	6.774%	$259.8559	$259.86	$259.85	$259.90
Purchase #7	$54.34	4.705%	$56.8967	$56.90	$56.90	$56.90
7 purchase totals =	$785.82		$841.9047	$841.91	$841.85	$842.00