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	$126.85	3.780%	$131.6449	$131.64	$131.65	$131.60
Purchase #2	$122.44	7.412%	$131.5153	$131.52	$131.50	$131.50
Purchase #3	$222.38	12.632%	$250.471	$250.47	$250.45	$250.50
Purchase #4	$59.67	5.489%	$62.9453	$62.95	$62.95	$62.90
Purchase #5	$78.76	4.815%	$82.5523	$82.55	$82.55	$82.60
Purchase #6	$173.70	7.551%	$186.8161	$186.82	$186.80	$186.80
Purchase #7	$41.26	8.764%	$44.876	$44.88	$44.90	$44.90
7 purchase totals =	$825.06		$890.8209	$890.83	$890.80	$890.80