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	$142.45	12.459%	$160.1978	$160.20	$160.20	$160.20
Purchase #2	$16.75	5.498%	$17.6709	$17.67	$17.65	$17.70
Purchase #3	$159.95	5.540%	$168.8112	$168.81	$168.80	$168.80
Purchase #4	$100.52	11.702%	$112.2829	$112.28	$112.30	$112.30
Purchase #5	$195.73	11.496%	$218.2311	$218.23	$218.25	$218.20
Purchase #6	$55.44	6.742%	$59.1778	$59.18	$59.20	$59.20
Purchase #7	$100.33	4.839%	$105.185	$105.19	$105.20	$105.20
7 purchase totals =	$771.17		$841.5567	$841.56	$841.60	$841.60