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	$84.87	4.246%	$88.4736	$88.47	$88.45	$88.50
Purchase #2	$55.51	4.317%	$57.9064	$57.91	$57.90	$57.90
Purchase #3	$211.82	11.208%	$235.5608	$235.56	$235.55	$235.60
Purchase #4	$165.25	12.641%	$186.1393	$186.14	$186.15	$186.10
Purchase #5	$68.78	8.780%	$74.8189	$74.82	$74.80	$74.80
Purchase #6	$250.55	12.597%	$282.1118	$282.11	$282.10	$282.10
Purchase #7	$80.95	11.841%	$90.5353	$90.54	$90.55	$90.50
7 purchase totals =	$917.73		$1,015.5461	$1,015.55	$1,015.50	$1,015.50