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	$123.48	10.424%	$136.3516	$136.35	$136.35	$136.40
Purchase #2	$211.44	10.391%	$233.4107	$233.41	$233.40	$233.40
Purchase #3	$79.94	7.356%	$85.8204	$85.82	$85.80	$85.80
Purchase #4	$152.70	11.204%	$169.8085	$169.81	$169.80	$169.80
Purchase #5	$159.61	13.752%	$181.5596	$181.56	$181.55	$181.60
Purchase #6	$194.47	10.279%	$214.4596	$214.46	$214.45	$214.50
Purchase #7	$154.41	13.210%	$174.8076	$174.81	$174.80	$174.80
7 purchase totals =	$1,076.05		$1,196.2180	$1,196.22	$1,196.15	$1,196.30