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	$133.26	13.182%	$150.8263	$150.83	$150.85	$150.80
Purchase #2	$90.51	10.165%	$99.7103	$99.71	$99.70	$99.70
Purchase #3	$73.96	8.789%	$80.4603	$80.46	$80.45	$80.50
Purchase #4	$236.41	13.308%	$267.8714	$267.87	$267.85	$267.90
Purchase #5	$77.88	4.448%	$81.3441	$81.34	$81.35	$81.30
Purchase #6	$77.50	10.868%	$85.9227	$85.92	$85.90	$85.90
Purchase #7	$80.51	9.536%	$88.1874	$88.19	$88.20	$88.20
7 purchase totals =	$770.03		$854.3225	$854.32	$854.30	$854.30