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	$219.89	6.669%	$234.5545	$234.55	$234.55	$234.60
Purchase #2	$55.50	6.434%	$59.0709	$59.07	$59.05	$59.10
Purchase #3	$112.31	11.394%	$125.1066	$125.11	$125.10	$125.10
Purchase #4	$55.76	12.258%	$62.5951	$62.60	$62.60	$62.60
Purchase #5	$91.77	6.633%	$97.8571	$97.86	$97.85	$97.90
Purchase #6	$28.47	13.714%	$32.3744	$32.37	$32.35	$32.40
Purchase #7	$46.86	5.321%	$49.3534	$49.35	$49.35	$49.40
7 purchase totals =	$610.56		$660.9120	$660.91	$660.85	$661.10