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	$121.64	9.562%	$133.2712	$133.27	$133.25	$133.30
Purchase #2	$214.37	6.726%	$228.7885	$228.79	$228.80	$228.80
Purchase #3	$185.87	5.809%	$196.6672	$196.67	$196.65	$196.70
Purchase #4	$66.54	9.485%	$72.8513	$72.85	$72.85	$72.90
Purchase #5	$83.61	11.414%	$93.1532	$93.15	$93.15	$93.20
Purchase #6	$162.33	7.758%	$174.9236	$174.92	$174.90	$174.90
Purchase #7	$182.26	9.632%	$199.8153	$199.82	$199.80	$199.80
7 purchase totals =	$1,016.62		$1,099.4703	$1,099.47	$1,099.40	$1,099.60