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	$111.87	5.728%	$118.2779	$118.28	$118.30	$118.30
Purchase #2	$83.92	6.458%	$89.3396	$89.34	$89.35	$89.30
Purchase #3	$165.43	12.252%	$185.6985	$185.70	$185.70	$185.70
Purchase #4	$69.86	8.661%	$75.9106	$75.91	$75.90	$75.90
Purchase #5	$84.96	5.689%	$89.7934	$89.79	$89.80	$89.80
Purchase #6	$195.98	4.718%	$205.2263	$205.23	$205.25	$205.20
Purchase #7	$81.80	13.512%	$92.8528	$92.85	$92.85	$92.90
7 purchase totals =	$793.82		$857.0991	$857.10	$857.15	$857.10