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	$171.46	4.582%	$179.3163	$179.32	$179.30	$179.30
Purchase #2	$224.38	6.291%	$238.4957	$238.50	$238.50	$238.50
Purchase #3	$123.84	8.123%	$133.8995	$133.90	$133.90	$133.90
Purchase #4	$182.37	7.715%	$196.4398	$196.44	$196.45	$196.40
Purchase #5	$172.28	13.869%	$196.1735	$196.17	$196.15	$196.20
Purchase #6	$30.92	6.259%	$32.8553	$32.86	$32.85	$32.90
Purchase #7	$243.86	12.426%	$274.162	$274.16	$274.15	$274.20
7 purchase totals =	$1,149.11		$1,251.3421	$1,251.35	$1,251.30	$1,251.40