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	$123.55	10.208%	$136.162	$136.16	$136.15	$136.20
Purchase #2	$237.34	7.802%	$255.8573	$255.86	$255.85	$255.90
Purchase #3	$73.79	11.390%	$82.1947	$82.19	$82.20	$82.20
Purchase #4	$67.93	8.689%	$73.8324	$73.83	$73.85	$73.80
Purchase #5	$175.98	5.143%	$185.0307	$185.03	$185.05	$185.00
Purchase #6	$203.45	4.627%	$212.8636	$212.86	$212.85	$212.90
Purchase #7	$159.61	13.700%	$181.4766	$181.48	$181.50	$181.50
7 purchase totals =	$1,041.65		$1,127.4173	$1,127.41	$1,127.45	$1,127.50