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	$83.51	3.362%	$86.3176	$86.32	$86.30	$86.30
Purchase #2	$213.77	5.500%	$225.5274	$225.53	$225.55	$225.50
Purchase #3	$46.83	11.871%	$52.3892	$52.39	$52.40	$52.40
Purchase #4	$54.67	9.610%	$59.9238	$59.92	$59.90	$59.90
Purchase #5	$168.95	6.236%	$179.4857	$179.49	$179.50	$179.50
Purchase #6	$70.27	3.289%	$72.5812	$72.58	$72.60	$72.60
Purchase #7	$225.38	13.117%	$254.9431	$254.94	$254.95	$254.90
7 purchase totals =	$863.38		$931.1680	$931.17	$931.20	$931.10