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	$92.85	6.805%	$99.1684	$99.17	$99.15	$99.20
Purchase #2	$210.72	6.257%	$223.9048	$223.90	$223.90	$223.90
Purchase #3	$97.98	4.136%	$102.0325	$102.03	$102.05	$102.00
Purchase #4	$134.85	12.760%	$152.0569	$152.06	$152.05	$152.10
Purchase #5	$154.32	12.863%	$174.1702	$174.17	$174.15	$174.20
Purchase #6	$201.50	4.268%	$210.1	$210.10	$210.10	$210.10
Purchase #7	$99.64	9.536%	$109.1417	$109.14	$109.15	$109.10
7 purchase totals =	$991.86		$1,070.5745	$1,070.57	$1,070.55	$1,070.60