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	$233.85	11.594%	$260.9626	$260.96	$260.95	$261.00
Purchase #2	$199.33	11.797%	$222.845	$222.85	$222.85	$222.80
Purchase #3	$129.59	4.476%	$135.3904	$135.39	$135.40	$135.40
Purchase #4	$6.76	12.512%	$7.6058	$7.61	$7.60	$7.60
Purchase #5	$89.86	10.717%	$99.4903	$99.49	$99.50	$99.50
Purchase #6	$111.69	4.814%	$117.0668	$117.07	$117.05	$117.10
Purchase #7	$147.59	7.359%	$158.4511	$158.45	$158.45	$158.50
7 purchase totals =	$918.67		$1,001.8120	$1,001.82	$1,001.80	$1,001.90