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	$86.83	13.545%	$98.5911	$98.59	$98.60	$98.60
Purchase #2	$90.27	8.467%	$97.9132	$97.91	$97.90	$97.90
Purchase #3	$89.93	7.168%	$96.3762	$96.38	$96.40	$96.40
Purchase #4	$118.81	8.500%	$128.9089	$128.91	$128.90	$128.90
Purchase #5	$180.60	6.134%	$191.678	$191.68	$191.70	$191.70
Purchase #6	$142.73	12.500%	$160.5713	$160.57	$160.55	$160.60
Purchase #7	$37.90	11.276%	$42.1736	$42.17	$42.15	$42.20
7 purchase totals =	$747.07		$816.2123	$816.21	$816.20	$816.30