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	$24.53	12.840%	$27.6797	$27.68	$27.70	$27.70
Purchase #2	$126.91	12.131%	$142.3055	$142.31	$142.30	$142.30
Purchase #3	$167.44	13.794%	$190.5367	$190.54	$190.55	$190.50
Purchase #4	$131.56	5.255%	$138.4735	$138.47	$138.45	$138.50
Purchase #5	$59.29	3.168%	$61.1683	$61.17	$61.15	$61.20
Purchase #6	$162.45	13.550%	$184.462	$184.46	$184.45	$184.50
Purchase #7	$113.57	12.873%	$128.1899	$128.19	$128.20	$128.20
7 purchase totals =	$785.75		$872.8156	$872.82	$872.80	$872.90