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	$78.59	9.297%	$85.8965	$85.90	$85.90	$85.90
Purchase #2	$171.88	9.125%	$187.5641	$187.56	$187.55	$187.60
Purchase #3	$56.81	10.482%	$62.7648	$62.76	$62.75	$62.80
Purchase #4	$113.95	12.828%	$128.5675	$128.57	$128.55	$128.60
Purchase #5	$181.70	11.753%	$203.0552	$203.06	$203.05	$203.10
Purchase #6	$70.75	10.362%	$78.0811	$78.08	$78.10	$78.10
Purchase #7	$39.47	3.355%	$40.7942	$40.79	$40.80	$40.80
7 purchase totals =	$713.15		$786.7234	$786.72	$786.70	$786.90