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	$120.44	9.534%	$131.9227	$131.92	$131.90	$131.90
Purchase #2	$52.96	8.138%	$57.2699	$57.27	$57.25	$57.30
Purchase #3	$214.49	4.181%	$223.4578	$223.46	$223.45	$223.50
Purchase #4	$100.60	7.560%	$108.2054	$108.21	$108.20	$108.20
Purchase #5	$223.78	8.673%	$243.1884	$243.19	$243.20	$243.20
Purchase #6	$115.90	12.385%	$130.2542	$130.25	$130.25	$130.30
Purchase #7	$84.45	7.262%	$90.5828	$90.58	$90.60	$90.60
7 purchase totals =	$912.62		$984.8812	$984.88	$984.85	$985.00