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	$132.85	10.653%	$147.0025	$147.00	$147.00	$147.00
Purchase #2	$60.31	11.269%	$67.1063	$67.11	$67.10	$67.10
Purchase #3	$57.33	3.292%	$59.2173	$59.22	$59.20	$59.20
Purchase #4	$182.99	6.594%	$195.0564	$195.06	$195.05	$195.10
Purchase #5	$12.82	5.382%	$13.51	$13.51	$13.50	$13.50
Purchase #6	$233.51	3.593%	$241.9	$241.90	$241.90	$241.90
Purchase #7	$79.37	8.216%	$85.891	$85.89	$85.90	$85.90
7 purchase totals =	$759.18		$809.6835	$809.69	$809.65	$809.70