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	$72.63	11.440%	$80.9389	$80.94	$80.95	$80.90
Purchase #2	$90.57	7.116%	$97.015	$97.02	$97.00	$97.00
Purchase #3	$89.37	12.733%	$100.7495	$100.75	$100.75	$100.70
Purchase #4	$161.41	3.558%	$167.153	$167.15	$167.15	$167.20
Purchase #5	$78.93	13.756%	$89.7876	$89.79	$89.80	$89.80
Purchase #6	$239.46	13.275%	$271.2483	$271.25	$271.25	$271.20
Purchase #7	$245.99	11.487%	$274.2469	$274.25	$274.25	$274.20
7 purchase totals =	$978.36		$1,081.1392	$1,081.15	$1,081.15	$1,081.00