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	$160.91	6.820%	$171.8841	$171.88	$171.90	$171.90
Purchase #2	$147.69	5.321%	$155.5486	$155.55	$155.55	$155.50
Purchase #3	$176.37	10.427%	$194.7601	$194.76	$194.75	$194.80
Purchase #4	$177.86	4.227%	$185.3781	$185.38	$185.40	$185.40
Purchase #5	$227.47	9.620%	$249.3526	$249.35	$249.35	$249.40
Purchase #6	$55.67	10.222%	$61.3606	$61.36	$61.35	$61.40
Purchase #7	$250.32	8.281%	$271.049	$271.05	$271.05	$271.00
7 purchase totals =	$1,196.29		$1,289.3331	$1,289.33	$1,289.35	$1,289.40