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	$240.65	12.539%	$270.8251	$270.83	$270.85	$270.80
Purchase #2	$65.43	3.518%	$67.7318	$67.73	$67.75	$67.70
Purchase #3	$71.39	12.260%	$80.1424	$80.14	$80.15	$80.10
Purchase #4	$123.26	6.798%	$131.6392	$131.64	$131.65	$131.60
Purchase #5	$142.90	10.209%	$157.4887	$157.49	$157.50	$157.50
Purchase #6	$112.32	12.414%	$126.2634	$126.26	$126.25	$126.30
Purchase #7	$25.59	8.860%	$27.8573	$27.86	$27.85	$27.90
7 purchase totals =	$781.54		$861.9479	$861.95	$862.00	$861.90