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	$73.63	10.696%	$81.5055	$81.51	$81.50	$81.50
Purchase #2	$62.33	8.107%	$67.3831	$67.38	$67.40	$67.40
Purchase #3	$249.54	7.342%	$267.8612	$267.86	$267.85	$267.90
Purchase #4	$35.47	8.214%	$38.3835	$38.38	$38.40	$38.40
Purchase #5	$22.26	4.384%	$23.2359	$23.24	$23.25	$23.20
Purchase #6	$167.86	10.405%	$185.3258	$185.33	$185.35	$185.30
Purchase #7	$92.86	8.291%	$100.559	$100.56	$100.55	$100.60
7 purchase totals =	$703.95		$764.2540	$764.26	$764.30	$764.30