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	$246.27	6.270%	$261.7111	$261.71	$261.70	$261.70
Purchase #2	$213.57	9.272%	$233.3722	$233.37	$233.35	$233.40
Purchase #3	$38.42	10.476%	$42.4449	$42.44	$42.45	$42.40
Purchase #4	$181.28	5.707%	$191.6256	$191.63	$191.65	$191.60
Purchase #5	$161.51	8.742%	$175.6292	$175.63	$175.65	$175.60
Purchase #6	$56.57	4.761%	$59.2633	$59.26	$59.25	$59.30
Purchase #7	$106.83	12.212%	$119.8761	$119.88	$119.90	$119.90
7 purchase totals =	$1,004.45		$1,083.9224	$1,083.92	$1,083.95	$1,083.90