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	$115.32	11.418%	$128.4872	$128.49	$128.50	$128.50
Purchase #2	$86.34	12.132%	$96.8148	$96.81	$96.80	$96.80
Purchase #3	$111.91	5.346%	$117.8927	$117.89	$117.90	$117.90
Purchase #4	$242.44	6.607%	$258.458	$258.46	$258.45	$258.50
Purchase #5	$118.42	3.751%	$122.8619	$122.86	$122.85	$122.90
Purchase #6	$94.41	5.399%	$99.5072	$99.51	$99.50	$99.50
Purchase #7	$53.37	8.299%	$57.7992	$57.80	$57.80	$57.80
7 purchase totals =	$822.21		$881.8210	$881.82	$881.80	$881.90