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	$121.98	7.503%	$131.1322	$131.13	$131.15	$131.10
Purchase #2	$98.32	10.401%	$108.5463	$108.55	$108.55	$108.50
Purchase #3	$231.59	6.150%	$245.8328	$245.83	$245.85	$245.80
Purchase #4	$110.88	5.462%	$116.9363	$116.94	$116.95	$116.90
Purchase #5	$102.69	6.281%	$109.14	$109.14	$109.15	$109.10
Purchase #6	$243.27	13.734%	$276.6807	$276.68	$276.70	$276.70
Purchase #7	$117.37	3.537%	$121.5214	$121.52	$121.50	$121.50
7 purchase totals =	$1,026.10		$1,109.7897	$1,109.79	$1,109.85	$1,109.60