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	$19.94	10.624%	$22.0584	$22.06	$22.05	$22.10
Purchase #2	$76.35	8.610%	$82.9237	$82.92	$82.90	$82.90
Purchase #3	$81.50	9.307%	$89.0852	$89.09	$89.10	$89.10
Purchase #4	$197.47	3.550%	$204.4802	$204.48	$204.50	$204.50
Purchase #5	$67.83	11.329%	$75.5145	$75.51	$75.50	$75.50
Purchase #6	$156.87	9.557%	$171.8621	$171.86	$171.85	$171.90
Purchase #7	$23.69	7.823%	$25.5433	$25.54	$25.55	$25.50
7 purchase totals =	$623.65		$671.4674	$671.46	$671.45	$671.50