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	$34.33	9.319%	$37.5292	$37.53	$37.55	$37.50
Purchase #2	$144.52	13.773%	$164.4247	$164.42	$164.40	$164.40
Purchase #3	$245.73	5.310%	$258.7783	$258.78	$258.80	$258.80
Purchase #4	$248.45	13.557%	$282.1324	$282.13	$282.15	$282.10
Purchase #5	$120.80	13.566%	$137.1877	$137.19	$137.20	$137.20
Purchase #6	$250.72	3.679%	$259.944	$259.94	$259.95	$259.90
Purchase #7	$249.70	12.691%	$281.3894	$281.39	$281.40	$281.40
7 purchase totals =	$1,294.25		$1,421.3857	$1,421.38	$1,421.45	$1,421.30