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	$247.75	11.118%	$275.2948	$275.29	$275.30	$275.30
Purchase #2	$39.89	7.374%	$42.8315	$42.83	$42.85	$42.80
Purchase #3	$17.59	3.604%	$18.2239	$18.22	$18.20	$18.20
Purchase #4	$57.59	13.473%	$65.3491	$65.35	$65.35	$65.30
Purchase #5	$144.50	8.566%	$156.8779	$156.88	$156.90	$156.90
Purchase #6	$110.25	11.666%	$123.1118	$123.11	$123.10	$123.10
Purchase #7	$159.54	5.169%	$167.7866	$167.79	$167.80	$167.80
7 purchase totals =	$777.11		$849.4756	$849.47	$849.50	$849.40