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	$104.48	13.136%	$118.2045	$118.20	$118.20	$118.20
Purchase #2	$49.97	5.853%	$52.8947	$52.89	$52.90	$52.90
Purchase #3	$203.91	10.777%	$225.8854	$225.89	$225.90	$225.90
Purchase #4	$96.34	5.808%	$101.9354	$101.94	$101.95	$101.90
Purchase #5	$247.57	7.374%	$265.8258	$265.83	$265.85	$265.80
Purchase #6	$65.65	11.148%	$72.9687	$72.97	$72.95	$73.00
Purchase #7	$76.56	8.131%	$82.7851	$82.79	$82.80	$82.80
7 purchase totals =	$844.48		$920.4996	$920.51	$920.55	$920.50