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	$6.68	12.699%	$7.5283	$7.53	$7.55	$7.50
Purchase #2	$106.59	9.498%	$116.7139	$116.71	$116.70	$116.70
Purchase #3	$181.91	6.681%	$194.0634	$194.06	$194.05	$194.10
Purchase #4	$107.69	7.663%	$115.9423	$115.94	$115.95	$115.90
Purchase #5	$96.45	9.219%	$105.3417	$105.34	$105.35	$105.30
Purchase #6	$134.72	7.323%	$144.5855	$144.59	$144.60	$144.60
Purchase #7	$26.76	6.222%	$28.425	$28.43	$28.45	$28.40
7 purchase totals =	$660.80		$712.6001	$712.60	$712.65	$712.50