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	$204.68	11.133%	$227.467	$227.47	$227.45	$227.50
Purchase #2	$250.42	13.732%	$284.8077	$284.81	$284.80	$284.80
Purchase #3	$56.74	9.843%	$62.3249	$62.32	$62.30	$62.30
Purchase #4	$49.26	3.802%	$51.1329	$51.13	$51.15	$51.10
Purchase #5	$120.80	8.654%	$131.254	$131.25	$131.25	$131.30
Purchase #6	$57.79	6.498%	$61.5452	$61.55	$61.55	$61.50
Purchase #7	$243.43	12.352%	$273.4985	$273.50	$273.50	$273.50
7 purchase totals =	$983.12		$1,092.0302	$1,092.03	$1,092.00	$1,092.00