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	$81.65	4.744%	$85.5235	$85.52	$85.50	$85.50
Purchase #2	$209.56	11.860%	$234.4138	$234.41	$234.40	$234.40
Purchase #3	$181.52	5.110%	$190.7957	$190.80	$190.80	$190.80
Purchase #4	$202.60	5.676%	$214.0996	$214.10	$214.10	$214.10
Purchase #5	$98.99	12.598%	$111.4608	$111.46	$111.45	$111.50
Purchase #6	$246.95	12.666%	$278.2287	$278.23	$278.25	$278.20
Purchase #7	$25.56	9.449%	$27.9752	$27.98	$28.00	$28.00
7 purchase totals =	$1,046.83		$1,142.4973	$1,142.50	$1,142.50	$1,142.50