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	$250.54	12.289%	$281.3289	$281.33	$281.35	$281.30
Purchase #2	$20.47	6.172%	$21.7334	$21.73	$21.75	$21.70
Purchase #3	$44.92	7.396%	$48.2423	$48.24	$48.25	$48.20
Purchase #4	$156.26	4.338%	$163.0386	$163.04	$163.05	$163.00
Purchase #5	$158.89	6.839%	$169.7565	$169.76	$169.75	$169.80
Purchase #6	$52.69	13.661%	$59.888	$59.89	$59.90	$59.90
Purchase #7	$41.71	8.566%	$45.2829	$45.28	$45.30	$45.30
7 purchase totals =	$725.48		$789.2706	$789.27	$789.35	$789.20