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	$88.37	12.181%	$99.1343	$99.13	$99.15	$99.10
Purchase #2	$146.66	3.791%	$152.2199	$152.22	$152.20	$152.20
Purchase #3	$228.35	7.167%	$244.7158	$244.72	$244.70	$244.70
Purchase #4	$128.89	10.688%	$142.6658	$142.67	$142.65	$142.70
Purchase #5	$31.45	6.357%	$33.4493	$33.45	$33.45	$33.40
Purchase #6	$221.50	12.835%	$249.9295	$249.93	$249.95	$249.90
Purchase #7	$164.76	9.292%	$180.0695	$180.07	$180.05	$180.10
7 purchase totals =	$1,009.98		$1,102.1841	$1,102.19	$1,102.15	$1,102.10