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	$228.51	3.853%	$237.3145	$237.31	$237.30	$237.30
Purchase #2	$142.28	5.793%	$150.5223	$150.52	$150.50	$150.50
Purchase #3	$162.99	13.215%	$184.5291	$184.53	$184.55	$184.50
Purchase #4	$246.59	7.666%	$265.4936	$265.49	$265.50	$265.50
Purchase #5	$209.52	11.335%	$233.2691	$233.27	$233.25	$233.30
Purchase #6	$64.52	9.853%	$70.8772	$70.88	$70.90	$70.90
Purchase #7	$180.58	8.640%	$196.1821	$196.18	$196.20	$196.20
7 purchase totals =	$1,234.99		$1,338.1879	$1,338.18	$1,338.20	$1,338.20