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	$159.48	13.833%	$181.5409	$181.54	$181.55	$181.50
Purchase #2	$64.67	11.134%	$71.8704	$71.87	$71.85	$71.90
Purchase #3	$98.78	5.840%	$104.5488	$104.55	$104.55	$104.50
Purchase #4	$110.28	5.110%	$115.9153	$115.92	$115.90	$115.90
Purchase #5	$90.85	9.216%	$99.2227	$99.22	$99.20	$99.20
Purchase #6	$131.66	9.670%	$144.3915	$144.39	$144.40	$144.40
Purchase #7	$154.29	5.614%	$162.9518	$162.95	$162.95	$163.00
7 purchase totals =	$810.01		$880.4414	$880.44	$880.40	$880.40