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	$73.89	6.677%	$78.8236	$78.82	$78.80	$78.80
Purchase #2	$141.42	3.342%	$146.1463	$146.15	$146.15	$146.10
Purchase #3	$116.49	3.607%	$120.6918	$120.69	$120.70	$120.70
Purchase #4	$85.28	9.787%	$93.6264	$93.63	$93.65	$93.60
Purchase #5	$24.28	13.410%	$27.5359	$27.54	$27.55	$27.50
Purchase #6	$94.63	4.750%	$99.1249	$99.12	$99.10	$99.10
Purchase #7	$199.88	4.467%	$208.8086	$208.81	$208.80	$208.80
7 purchase totals =	$735.87		$774.7575	$774.76	$774.75	$774.60