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	$40.89	3.873%	$42.4737	$42.47	$42.45	$42.50
Purchase #2	$55.39	10.609%	$61.2663	$61.27	$61.25	$61.30
Purchase #3	$98.48	4.754%	$103.1617	$103.16	$103.15	$103.20
Purchase #4	$240.64	7.776%	$259.3522	$259.35	$259.35	$259.40
Purchase #5	$244.44	3.541%	$253.0956	$253.10	$253.10	$253.10
Purchase #6	$245.55	12.260%	$275.6544	$275.65	$275.65	$275.70
Purchase #7	$144.53	13.869%	$164.5749	$164.57	$164.55	$164.60
7 purchase totals =	$1,069.92		$1,159.5788	$1,159.57	$1,159.50	$1,159.80