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	$18.55	11.550%	$20.6925	$20.69	$20.70	$20.70
Purchase #2	$54.62	4.861%	$57.2751	$57.28	$57.30	$57.30
Purchase #3	$236.95	11.427%	$264.0263	$264.03	$264.05	$264.00
Purchase #4	$89.62	10.409%	$98.9485	$98.95	$98.95	$98.90
Purchase #5	$119.38	7.775%	$128.6618	$128.66	$128.65	$128.70
Purchase #6	$132.67	5.843%	$140.4219	$140.42	$140.40	$140.40
Purchase #7	$82.25	8.599%	$89.3227	$89.32	$89.30	$89.30
7 purchase totals =	$734.04		$799.3488	$799.35	$799.35	$799.30