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	$90.98	10.247%	$100.3027	$100.30	$100.30	$100.30
Purchase #2	$121.34	5.563%	$128.0901	$128.09	$128.10	$128.10
Purchase #3	$63.36	12.712%	$71.4143	$71.41	$71.40	$71.40
Purchase #4	$35.92	4.783%	$37.6381	$37.64	$37.65	$37.60
Purchase #5	$138.81	5.474%	$146.4085	$146.41	$146.40	$146.40
Purchase #6	$224.92	12.789%	$253.685	$253.69	$253.70	$253.70
Purchase #7	$131.40	6.719%	$140.2288	$140.23	$140.25	$140.20
7 purchase totals =	$806.73		$877.7675	$877.77	$877.80	$877.70