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	$7.29	7.276%	$7.8204	$7.82	$7.80	$7.80
Purchase #2	$49.67	6.369%	$52.8335	$52.83	$52.85	$52.80
Purchase #3	$13.85	5.648%	$14.6322	$14.63	$14.65	$14.60
Purchase #4	$39.80	5.727%	$42.0793	$42.08	$42.10	$42.10
Purchase #5	$198.61	7.775%	$214.0519	$214.05	$214.05	$214.10
Purchase #6	$136.33	8.483%	$147.8949	$147.89	$147.90	$147.90
Purchase #7	$47.32	13.235%	$53.5828	$53.58	$53.60	$53.60
7 purchase totals =	$492.87		$532.8950	$532.88	$532.95	$532.90