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	$32.80	10.171%	$36.1361	$36.14	$36.15	$36.10
Purchase #2	$103.38	6.270%	$109.8619	$109.86	$109.85	$109.90
Purchase #3	$131.72	4.642%	$137.8344	$137.83	$137.85	$137.80
Purchase #4	$148.53	3.870%	$154.2781	$154.28	$154.30	$154.30
Purchase #5	$81.28	4.571%	$84.9953	$85.00	$85.00	$85.00
Purchase #6	$214.39	7.254%	$229.9419	$229.94	$229.95	$229.90
Purchase #7	$190.46	3.279%	$196.7052	$196.71	$196.70	$196.70
7 purchase totals =	$902.56		$949.7529	$949.76	$949.80	$949.70