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	$52.35	10.662%	$57.9316	$57.93	$57.95	$57.90
Purchase #2	$130.35	12.708%	$146.9149	$146.91	$146.90	$146.90
Purchase #3	$93.52	8.547%	$101.5132	$101.51	$101.50	$101.50
Purchase #4	$10.31	11.651%	$11.5112	$11.51	$11.50	$11.50
Purchase #5	$60.89	4.315%	$63.5174	$63.52	$63.50	$63.50
Purchase #6	$120.78	8.592%	$131.1574	$131.16	$131.15	$131.20
Purchase #7	$26.41	4.601%	$27.6251	$27.63	$27.65	$27.60
7 purchase totals =	$494.61		$540.1708	$540.17	$540.15	$540.10