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	$115.27	13.797%	$131.1738	$131.17	$131.15	$131.20
Purchase #2	$57.83	11.606%	$64.5417	$64.54	$64.55	$64.50
Purchase #3	$155.51	7.817%	$167.6662	$167.67	$167.65	$167.70
Purchase #4	$135.30	8.749%	$147.1374	$147.14	$147.15	$147.10
Purchase #5	$117.74	12.674%	$132.6624	$132.66	$132.65	$132.70
Purchase #6	$48.79	12.473%	$54.8756	$54.88	$54.90	$54.90
Purchase #7	$95.82	8.309%	$103.7817	$103.78	$103.80	$103.80
7 purchase totals =	$726.26		$801.8388	$801.84	$801.85	$801.90