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	$137.86	4.112%	$143.5288	$143.53	$143.55	$143.50
Purchase #2	$144.59	10.290%	$159.4683	$159.47	$159.45	$159.50
Purchase #3	$88.96	12.577%	$100.1485	$100.15	$100.15	$100.10
Purchase #4	$184.78	6.243%	$196.3158	$196.32	$196.30	$196.30
Purchase #5	$243.36	5.279%	$256.207	$256.21	$256.20	$256.20
Purchase #6	$125.32	12.371%	$140.8233	$140.82	$140.80	$140.80
Purchase #7	$245.27	6.445%	$261.0777	$261.08	$261.10	$261.10
7 purchase totals =	$1,170.14		$1,257.5694	$1,257.58	$1,257.55	$1,257.50