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	$105.88	9.443%	$115.8782	$115.88	$115.90	$115.90
Purchase #2	$46.69	12.550%	$52.5496	$52.55	$52.55	$52.50
Purchase #3	$20.46	8.412%	$22.1811	$22.18	$22.20	$22.20
Purchase #4	$126.81	9.551%	$138.9216	$138.92	$138.90	$138.90
Purchase #5	$138.55	6.380%	$147.3895	$147.39	$147.40	$147.40
Purchase #6	$56.60	4.783%	$59.3072	$59.31	$59.30	$59.30
Purchase #7	$63.72	5.355%	$67.1322	$67.13	$67.15	$67.10
7 purchase totals =	$558.71		$603.3594	$603.36	$603.40	$603.30