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	$224.47	6.296%	$238.6026	$238.60	$238.60	$238.60
Purchase #2	$177.98	10.585%	$196.8192	$196.82	$196.80	$196.80
Purchase #3	$130.36	4.506%	$136.234	$136.23	$136.25	$136.20
Purchase #4	$162.89	4.266%	$169.8389	$169.84	$169.85	$169.80
Purchase #5	$103.25	3.382%	$106.7419	$106.74	$106.75	$106.70
Purchase #6	$71.87	8.834%	$78.219	$78.22	$78.20	$78.20
Purchase #7	$113.69	12.484%	$127.8831	$127.88	$127.90	$127.90
7 purchase totals =	$984.51		$1,054.3387	$1,054.33	$1,054.35	$1,054.20