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	$211.92	10.790%	$234.7862	$234.79	$234.80	$234.80
Purchase #2	$146.55	12.194%	$164.4203	$164.42	$164.40	$164.40
Purchase #3	$30.61	12.774%	$34.5201	$34.52	$34.50	$34.50
Purchase #4	$182.96	11.777%	$204.5072	$204.51	$204.50	$204.50
Purchase #5	$66.54	8.293%	$72.0582	$72.06	$72.05	$72.10
Purchase #6	$225.71	3.576%	$233.7814	$233.78	$233.80	$233.80
Purchase #7	$37.49	12.314%	$42.1065	$42.11	$42.10	$42.10
7 purchase totals =	$901.78		$986.1799	$986.19	$986.15	$986.20