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	$30.96	8.668%	$33.6436	$33.64	$33.65	$33.60
Purchase #2	$105.72	5.313%	$111.3369	$111.34	$111.35	$111.30
Purchase #3	$208.42	7.402%	$223.8472	$223.85	$223.85	$223.80
Purchase #4	$82.46	3.152%	$85.0591	$85.06	$85.05	$85.10
Purchase #5	$221.66	3.216%	$228.7886	$228.79	$228.80	$228.80
Purchase #6	$236.49	6.459%	$251.7649	$251.76	$251.75	$251.80
Purchase #7	$54.78	4.408%	$57.1947	$57.19	$57.20	$57.20
7 purchase totals =	$940.49		$991.6350	$991.63	$991.65	$991.60