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	$143.93	11.454%	$160.4157	$160.42	$160.40	$160.40
Purchase #2	$205.61	13.555%	$233.4804	$233.48	$233.50	$233.50
Purchase #3	$222.57	6.700%	$237.4822	$237.48	$237.50	$237.50
Purchase #4	$145.55	3.665%	$150.8844	$150.88	$150.90	$150.90
Purchase #5	$56.84	7.668%	$61.1985	$61.20	$61.20	$61.20
Purchase #6	$86.66	13.727%	$98.5558	$98.56	$98.55	$98.60
Purchase #7	$169.95	12.109%	$190.5292	$190.53	$190.55	$190.50
7 purchase totals =	$1,031.11		$1,132.5462	$1,132.55	$1,132.60	$1,132.60