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	$228.57	9.663%	$250.6567	$250.66	$250.65	$250.70
Purchase #2	$146.43	9.686%	$160.6132	$160.61	$160.60	$160.60
Purchase #3	$164.31	4.157%	$171.1404	$171.14	$171.15	$171.10
Purchase #4	$144.54	9.582%	$158.3898	$158.39	$158.40	$158.40
Purchase #5	$112.82	12.471%	$126.8898	$126.89	$126.90	$126.90
Purchase #6	$199.37	4.831%	$209.0016	$209.00	$209.00	$209.00
Purchase #7	$223.82	5.516%	$236.1659	$236.17	$236.15	$236.20
7 purchase totals =	$1,219.86		$1,312.8574	$1,312.86	$1,312.85	$1,312.90