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	$112.64	6.837%	$120.3412	$120.34	$120.35	$120.30
Purchase #2	$177.85	12.748%	$200.5223	$200.52	$200.50	$200.50
Purchase #3	$74.73	10.284%	$82.4152	$82.42	$82.40	$82.40
Purchase #4	$249.73	8.681%	$271.4091	$271.41	$271.40	$271.40
Purchase #5	$190.69	10.751%	$211.1911	$211.19	$211.20	$211.20
Purchase #6	$210.64	13.327%	$238.712	$238.71	$238.70	$238.70
Purchase #7	$51.31	13.142%	$58.0532	$58.05	$58.05	$58.10
7 purchase totals =	$1,067.59		$1,182.6441	$1,182.64	$1,182.60	$1,182.60