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	$196.59	13.424%	$222.9802	$222.98	$223.00	$223.00
Purchase #2	$161.94	7.858%	$174.6652	$174.67	$174.65	$174.70
Purchase #3	$165.63	9.819%	$181.8932	$181.89	$181.90	$181.90
Purchase #4	$236.84	10.585%	$261.9095	$261.91	$261.90	$261.90
Purchase #5	$149.72	5.236%	$157.5593	$157.56	$157.55	$157.60
Purchase #6	$66.86	8.239%	$72.3686	$72.37	$72.35	$72.40
Purchase #7	$243.82	9.851%	$267.8387	$267.84	$267.85	$267.80
7 purchase totals =	$1,221.40		$1,339.2147	$1,339.22	$1,339.20	$1,339.30