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	$50.73	8.580%	$55.0826	$55.08	$55.10	$55.10
Purchase #2	$116.96	12.384%	$131.4443	$131.44	$131.45	$131.40
Purchase #3	$59.53	9.285%	$65.0574	$65.06	$65.05	$65.10
Purchase #4	$229.31	3.653%	$237.6867	$237.69	$237.70	$237.70
Purchase #5	$45.98	3.549%	$47.6118	$47.61	$47.60	$47.60
Purchase #6	$131.59	6.864%	$140.6223	$140.62	$140.60	$140.60
Purchase #7	$158.70	5.424%	$167.3079	$167.31	$167.30	$167.30
7 purchase totals =	$792.80		$844.8130	$844.81	$844.80	$844.80