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	$7.33	7.148%	$7.8539	$7.85	$7.85	$7.90
Purchase #2	$21.25	9.361%	$23.2392	$23.24	$23.25	$23.20
Purchase #3	$10.46	9.684%	$11.4729	$11.47	$11.45	$11.50
Purchase #4	$97.54	3.499%	$100.9529	$100.95	$100.95	$101.00
Purchase #5	$63.57	3.637%	$65.882	$65.88	$65.90	$65.90
Purchase #6	$182.35	11.815%	$203.8947	$203.89	$203.90	$203.90
Purchase #7	$103.28	4.802%	$108.2395	$108.24	$108.25	$108.20
7 purchase totals =	$485.78		$521.5351	$521.52	$521.55	$521.60