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	$63.34	12.155%	$71.039	$71.04	$71.05	$71.00
Purchase #2	$52.65	3.728%	$54.6128	$54.61	$54.60	$54.60
Purchase #3	$53.69	7.780%	$57.8671	$57.87	$57.85	$57.90
Purchase #4	$234.41	7.470%	$251.9204	$251.92	$251.90	$251.90
Purchase #5	$184.95	5.791%	$195.6605	$195.66	$195.65	$195.70
Purchase #6	$28.50	11.646%	$31.8191	$31.82	$31.80	$31.80
Purchase #7	$6.33	8.557%	$6.8717	$6.87	$6.85	$6.90
7 purchase totals =	$623.87		$669.7906	$669.79	$669.70	$669.80