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	$20.48	3.366%	$21.1694	$21.17	$21.15	$21.20
Purchase #2	$118.55	8.796%	$128.9777	$128.98	$129.00	$129.00
Purchase #3	$146.63	11.541%	$163.5526	$163.55	$163.55	$163.60
Purchase #4	$5.89	11.194%	$6.5493	$6.55	$6.55	$6.50
Purchase #5	$10.65	11.817%	$11.9085	$11.91	$11.90	$11.90
Purchase #6	$42.31	12.417%	$47.5636	$47.56	$47.55	$47.60
Purchase #7	$80.82	11.205%	$89.8759	$89.88	$89.90	$89.90
7 purchase totals =	$425.33		$469.5970	$469.60	$469.60	$469.70