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	$40.40	9.524%	$44.2477	$44.25	$44.25	$44.20
Purchase #2	$93.54	5.336%	$98.5313	$98.53	$98.55	$98.50
Purchase #3	$238.69	6.648%	$254.5581	$254.56	$254.55	$254.60
Purchase #4	$43.55	12.183%	$48.8557	$48.86	$48.85	$48.90
Purchase #5	$229.51	12.529%	$258.2653	$258.27	$258.25	$258.30
Purchase #6	$155.78	4.565%	$162.8914	$162.89	$162.90	$162.90
Purchase #7	$30.69	8.639%	$33.3413	$33.34	$33.35	$33.30
7 purchase totals =	$832.16		$900.6908	$900.70	$900.70	$900.70