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	$61.87	12.556%	$69.6384	$69.64	$69.65	$69.60
Purchase #2	$137.33	4.738%	$143.8367	$143.84	$143.85	$143.80
Purchase #3	$92.59	7.264%	$99.3157	$99.32	$99.30	$99.30
Purchase #4	$138.41	8.632%	$150.3576	$150.36	$150.35	$150.40
Purchase #5	$180.84	8.489%	$196.1915	$196.19	$196.20	$196.20
Purchase #6	$35.47	11.597%	$39.5835	$39.58	$39.60	$39.60
Purchase #7	$188.47	5.559%	$198.947	$198.95	$198.95	$198.90
7 purchase totals =	$834.98		$897.8704	$897.88	$897.90	$897.80