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	$136.38	11.802%	$152.4756	$152.48	$152.50	$152.50
Purchase #2	$204.89	5.568%	$216.2983	$216.30	$216.30	$216.30
Purchase #3	$116.89	5.553%	$123.3809	$123.38	$123.40	$123.40
Purchase #4	$156.57	4.754%	$164.0133	$164.01	$164.00	$164.00
Purchase #5	$72.51	10.795%	$80.3375	$80.34	$80.35	$80.30
Purchase #6	$209.55	9.302%	$229.0423	$229.04	$229.05	$229.00
Purchase #7	$159.83	10.403%	$176.4571	$176.46	$176.45	$176.50
7 purchase totals =	$1,056.62		$1,142.0050	$1,142.01	$1,142.05	$1,142.00