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	$60.63	3.607%	$62.8169	$62.82	$62.80	$62.80
Purchase #2	$76.72	4.673%	$80.3051	$80.31	$80.30	$80.30
Purchase #3	$229.76	11.699%	$256.6396	$256.64	$256.65	$256.60
Purchase #4	$29.28	6.568%	$31.2031	$31.20	$31.20	$31.20
Purchase #5	$79.43	12.529%	$89.3818	$89.38	$89.40	$89.40
Purchase #6	$72.48	10.285%	$79.9346	$79.93	$79.95	$79.90
Purchase #7	$61.76	5.539%	$65.1809	$65.18	$65.20	$65.20
7 purchase totals =	$610.06		$665.4620	$665.46	$665.50	$665.40