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	$56.46	3.789%	$58.5993	$58.60	$58.60	$58.60
Purchase #2	$243.59	8.705%	$264.7945	$264.79	$264.80	$264.80
Purchase #3	$235.36	6.564%	$250.809	$250.81	$250.80	$250.80
Purchase #4	$229.30	13.306%	$259.8107	$259.81	$259.80	$259.80
Purchase #5	$136.59	3.535%	$141.4185	$141.42	$141.40	$141.40
Purchase #6	$190.28	12.549%	$214.1582	$214.16	$214.15	$214.20
Purchase #7	$81.80	9.411%	$89.4982	$89.50	$89.50	$89.50
7 purchase totals =	$1,173.38		$1,279.0884	$1,279.09	$1,279.05	$1,279.10