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	$45.67	11.465%	$50.9061	$50.91	$50.90	$50.90
Purchase #2	$93.71	9.549%	$102.6584	$102.66	$102.65	$102.70
Purchase #3	$188.34	4.544%	$196.8982	$196.90	$196.90	$196.90
Purchase #4	$14.61	4.527%	$15.2714	$15.27	$15.25	$15.30
Purchase #5	$131.69	11.294%	$146.5631	$146.56	$146.55	$146.60
Purchase #6	$162.61	11.468%	$181.2581	$181.26	$181.25	$181.30
Purchase #7	$174.55	5.529%	$184.2009	$184.20	$184.20	$184.20
7 purchase totals =	$811.18		$877.7562	$877.76	$877.70	$877.90