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	$81.53	10.709%	$90.261	$90.26	$90.25	$90.30
Purchase #2	$62.92	11.455%	$70.1275	$70.13	$70.15	$70.10
Purchase #3	$98.62	8.181%	$106.6881	$106.69	$106.70	$106.70
Purchase #4	$51.71	7.170%	$55.4176	$55.42	$55.40	$55.40
Purchase #5	$218.32	9.437%	$238.9229	$238.92	$238.90	$238.90
Purchase #6	$135.78	6.370%	$144.4292	$144.43	$144.45	$144.40
Purchase #7	$144.93	5.108%	$152.333	$152.33	$152.35	$152.30
7 purchase totals =	$793.81		$858.1793	$858.18	$858.20	$858.10