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	$119.91	9.443%	$131.2331	$131.23	$131.25	$131.20
Purchase #2	$84.99	6.819%	$90.7855	$90.79	$90.80	$90.80
Purchase #3	$96.28	4.283%	$100.4037	$100.40	$100.40	$100.40
Purchase #4	$43.97	5.299%	$46.3	$46.30	$46.30	$46.30
Purchase #5	$60.63	9.755%	$66.5445	$66.54	$66.55	$66.50
Purchase #6	$70.94	13.120%	$80.2473	$80.25	$80.25	$80.20
Purchase #7	$222.62	12.346%	$250.1047	$250.10	$250.10	$250.10
7 purchase totals =	$699.34		$765.6188	$765.61	$765.65	$765.50