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	$100.26	13.102%	$113.3961	$113.40	$113.40	$113.40
Purchase #2	$159.49	4.642%	$166.8935	$166.89	$166.90	$166.90
Purchase #3	$104.95	7.571%	$112.8958	$112.90	$112.90	$112.90
Purchase #4	$60.47	11.681%	$67.5335	$67.53	$67.55	$67.50
Purchase #5	$16.31	8.465%	$17.6906	$17.69	$17.70	$17.70
Purchase #6	$82.43	3.316%	$85.1634	$85.16	$85.15	$85.20
Purchase #7	$124.96	11.567%	$139.4141	$139.41	$139.40	$139.40
7 purchase totals =	$648.87		$702.9870	$702.98	$703.00	$703.00