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	$54.36	12.329%	$61.062	$61.06	$61.05	$61.10
Purchase #2	$70.62	10.658%	$78.1467	$78.15	$78.15	$78.10
Purchase #3	$39.92	13.780%	$45.421	$45.42	$45.40	$45.40
Purchase #4	$191.64	11.595%	$213.8607	$213.86	$213.85	$213.90
Purchase #5	$88.98	8.353%	$96.4125	$96.41	$96.40	$96.40
Purchase #6	$167.43	12.203%	$187.8615	$187.86	$187.85	$187.90
Purchase #7	$133.77	11.403%	$149.0238	$149.02	$149.00	$149.00
7 purchase totals =	$746.72		$831.7882	$831.78	$831.70	$831.80