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	$204.89	9.104%	$223.5432	$223.54	$223.55	$223.50
Purchase #2	$58.72	6.409%	$62.4834	$62.48	$62.50	$62.50
Purchase #3	$244.52	9.729%	$268.3094	$268.31	$268.30	$268.30
Purchase #4	$92.82	9.633%	$101.7614	$101.76	$101.75	$101.80
Purchase #5	$89.33	7.514%	$96.0423	$96.04	$96.05	$96.00
Purchase #6	$73.73	9.372%	$80.64	$80.64	$80.65	$80.60
Purchase #7	$104.60	10.314%	$115.3884	$115.39	$115.40	$115.40
7 purchase totals =	$868.61		$948.1681	$948.16	$948.20	$948.10