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	$171.81	6.750%	$183.4072	$183.41	$183.40	$183.40
Purchase #2	$134.33	6.153%	$142.5953	$142.60	$142.60	$142.60
Purchase #3	$176.67	4.349%	$184.3534	$184.35	$184.35	$184.40
Purchase #4	$207.85	12.540%	$233.9144	$233.91	$233.90	$233.90
Purchase #5	$30.38	7.796%	$32.7484	$32.75	$32.75	$32.70
Purchase #6	$250.43	6.662%	$267.1136	$267.11	$267.10	$267.10
Purchase #7	$136.60	11.638%	$152.4975	$152.50	$152.50	$152.50
7 purchase totals =	$1,108.07		$1,196.6298	$1,196.63	$1,196.60	$1,196.60