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	$82.70	9.453%	$90.5176	$90.52	$90.50	$90.50
Purchase #2	$67.73	5.847%	$71.6902	$71.69	$71.70	$71.70
Purchase #3	$228.38	7.774%	$246.1343	$246.13	$246.15	$246.10
Purchase #4	$229.37	5.560%	$242.123	$242.12	$242.10	$242.10
Purchase #5	$24.29	13.371%	$27.5378	$27.54	$27.55	$27.50
Purchase #6	$110.48	4.186%	$115.1047	$115.10	$115.10	$115.10
Purchase #7	$18.31	8.709%	$19.9046	$19.90	$19.90	$19.90
7 purchase totals =	$761.26		$813.0122	$813.00	$813.00	$812.90