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	$111.84	11.399%	$124.5886	$124.59	$124.60	$124.60
Purchase #2	$38.46	6.311%	$40.8872	$40.89	$40.90	$40.90
Purchase #3	$250.90	7.456%	$269.6071	$269.61	$269.60	$269.60
Purchase #4	$32.70	6.725%	$34.8991	$34.90	$34.90	$34.90
Purchase #5	$174.78	8.586%	$189.7866	$189.79	$189.80	$189.80
Purchase #6	$92.52	11.274%	$102.9507	$102.95	$102.95	$103.00
Purchase #7	$43.48	8.757%	$47.2875	$47.29	$47.30	$47.30
7 purchase totals =	$744.68		$810.0068	$810.02	$810.05	$810.10