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	$109.53	6.638%	$116.8006	$116.80	$116.80	$116.80
Purchase #2	$42.74	5.580%	$45.1249	$45.12	$45.10	$45.10
Purchase #3	$136.26	11.184%	$151.4993	$151.50	$151.50	$151.50
Purchase #4	$92.84	7.666%	$99.9571	$99.96	$99.95	$100.00
Purchase #5	$244.27	12.374%	$274.496	$274.50	$274.50	$274.50
Purchase #6	$250.31	12.340%	$281.1983	$281.20	$281.20	$281.20
Purchase #7	$141.54	5.534%	$149.3728	$149.37	$149.35	$149.40
7 purchase totals =	$1,017.49		$1,118.4490	$1,118.45	$1,118.40	$1,118.50