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	$92.56	12.468%	$104.1004	$104.10	$104.10	$104.10
Purchase #2	$105.90	6.680%	$112.9741	$112.97	$112.95	$113.00
Purchase #3	$41.39	12.234%	$46.4537	$46.45	$46.45	$46.50
Purchase #4	$203.90	7.639%	$219.4759	$219.48	$219.50	$219.50
Purchase #5	$225.72	7.707%	$243.1162	$243.12	$243.10	$243.10
Purchase #6	$10.40	11.126%	$11.5571	$11.56	$11.55	$11.60
Purchase #7	$91.85	11.555%	$102.4633	$102.46	$102.45	$102.50
7 purchase totals =	$771.72		$840.1407	$840.14	$840.10	$840.30