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	$31.64	3.638%	$32.7911	$32.79	$32.80	$32.80
Purchase #2	$241.89	9.739%	$265.4477	$265.45	$265.45	$265.40
Purchase #3	$39.47	4.578%	$41.2769	$41.28	$41.30	$41.30
Purchase #4	$61.27	7.433%	$65.8242	$65.82	$65.80	$65.80
Purchase #5	$82.94	9.609%	$90.9097	$90.91	$90.90	$90.90
Purchase #6	$243.59	4.327%	$254.1301	$254.13	$254.15	$254.10
Purchase #7	$78.61	11.646%	$87.7649	$87.76	$87.75	$87.80
7 purchase totals =	$779.41		$838.1446	$838.14	$838.15	$838.10