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	$199.33	11.616%	$222.4842	$222.48	$222.50	$222.50
Purchase #2	$46.79	7.793%	$50.4363	$50.44	$50.45	$50.40
Purchase #3	$98.90	7.363%	$106.182	$106.18	$106.20	$106.20
Purchase #4	$19.38	3.191%	$19.9984	$20.00	$20.00	$20.00
Purchase #5	$114.86	13.712%	$130.6096	$130.61	$130.60	$130.60
Purchase #6	$219.43	13.842%	$249.8035	$249.80	$249.80	$249.80
Purchase #7	$52.42	13.265%	$59.3735	$59.37	$59.35	$59.40
7 purchase totals =	$751.11		$838.8875	$838.88	$838.90	$838.90