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	$113.57	9.455%	$124.308	$124.31	$124.30	$124.30
Purchase #2	$197.38	3.482%	$204.2528	$204.25	$204.25	$204.30
Purchase #3	$152.65	5.723%	$161.3862	$161.39	$161.40	$161.40
Purchase #4	$61.92	5.799%	$65.5107	$65.51	$65.50	$65.50
Purchase #5	$31.49	3.811%	$32.6901	$32.69	$32.70	$32.70
Purchase #6	$97.78	7.736%	$105.3443	$105.34	$105.35	$105.30
Purchase #7	$75.32	13.365%	$85.3865	$85.39	$85.40	$85.40
7 purchase totals =	$730.11		$778.8786	$778.88	$778.90	$778.90