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	$122.91	11.781%	$137.39	$137.39	$137.40	$137.40
Purchase #2	$82.51	12.780%	$93.0548	$93.05	$93.05	$93.10
Purchase #3	$30.85	4.112%	$32.1186	$32.12	$32.10	$32.10
Purchase #4	$32.46	13.873%	$36.9632	$36.96	$36.95	$37.00
Purchase #5	$164.50	9.782%	$180.5914	$180.59	$180.60	$180.60
Purchase #6	$225.34	7.340%	$241.88	$241.88	$241.90	$241.90
Purchase #7	$234.54	10.372%	$258.8665	$258.87	$258.85	$258.90
7 purchase totals =	$893.11		$980.8645	$980.86	$980.85	$981.00