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	$186.72	11.485%	$208.1648	$208.16	$208.15	$208.20
Purchase #2	$250.77	10.774%	$277.788	$277.79	$277.80	$277.80
Purchase #3	$72.43	13.643%	$82.3116	$82.31	$82.30	$82.30
Purchase #4	$30.90	9.410%	$33.8077	$33.81	$33.80	$33.80
Purchase #5	$193.40	5.370%	$203.7856	$203.79	$203.80	$203.80
Purchase #6	$142.57	13.323%	$161.5646	$161.56	$161.55	$161.60
Purchase #7	$67.41	6.833%	$72.0161	$72.02	$72.00	$72.00
7 purchase totals =	$944.20		$1,039.4384	$1,039.44	$1,039.40	$1,039.50